The answer to this question is dependent somewhat on your understanding of the motivations of France, the United Kingdom, Germany, Belgium and Portugal for seeking, expanding or consolidating colonial possessions in Asia and Africa in the latter half of the 19th Century.
The 19th Century British historian J.R. Seeley is often quoted for his statement that Britain acquired its modern empire in a "fit of absence of mind" (the same sentiment is sometimes attributed to other 19th Century British speakers). There are later historians who have agreed somewhat with Seeley's characterization, most explicitly Bernard Porter, but Ronald Robinson & Jack Gallagher's theory of "peripheral imperialism" in their book Africa and the Victorians has echoes of it. R&G argued that imperialism wasn't a single policy decision made coherently by European governments who had clear aims, but instead was the reluctant acquiescence of European governments to actions taken independently over decades by their civil servants, soldiers, and citizens in various locations across Africa, the Middle East and Asia. I personally think there's a lot that is valid about this interpretation, and I'll come back to its implications in a minute.
But alternatively, there are many historians who see the rise of modern imperialism as driven primarily by the needs and nature of extractive capitalism, again with governments essentially along for the ride. In an African context, Walter Rodney's How Europe Underdeveloped Africa is one of the clearest statements of this perspective. Another body of thought sees imperialism as a result of the full formation of modern white supremacy--a cultural and ideological formation that pushed towards imperial domination. And there are definitely scholars who still see modern imperialism primarily as a diplomatic-political consequence of rivalries between European nation-states, essentially as an early expression of the systems and pressures that eventually led to World War I.
So whether European governments involved in imperialism looked ahead to see decolonization as a prospect, thus raising questions about how they calculated the risk and reward of imperial rule, depends significantly on whether you thought they were calculating and rational in their actions and whether their deliberate plans were actually a major cause of the spread of imperial power. If, for example, you emphasize the role of extractive capitalism, as in the Congo Free State, the Witwatersrand or the Copperbelt, you would be looking at a very different calculus of risk. Leopold II didn't really worry about what would happen next in Congo at all: the way that chartered companies in Congo approached rubber extraction was rapacious, destructive, and quintessentially short-term. Even in situations where extraction took the development of infrastructure and the recruitment of a skilled labor force, companies and executives were generally only interested in those aspects of imperial administration that they saw as directly necessary for the survival of their enterprises.
If you are inclined to think that imperialism was a calculated, centralized decision, I think you could fairly say that the major individuals involved in its establishment in the late 19th Century had inconsistent thoughts at best about how long they could sustain imperial rule--in part because they had become ideologically and politically reliant on the idea of their empires. Think of it this way: somewhere deep inside the U.S. government's operations in the early 2000s, there were plenty of individuals in a range of departments arguing in expert ways that the US invasion of Iraq was a mistake, that the occupation of Iraq would quickly be unsustainable, and that a plan for an exit was urgently needed. We even know who these people were--but we also know that most of their expertise never floated up into Cabinet meetings because a set of political actors systematically suppressed, purged, diverted or derogated that expertise for ideological reasons.
If you believe in any version of the "absence of mind" interpretation, you don't think that some centralized, rational institution made a singular decision to pursue imperial rule. So the answer to your question takes a modification of the question. Essentially, I think, to the following: At what point did imperial administrators or European governments begin to think about or talk about decolonization once they had created these new colonial states, and how did that affect the ideological claims they were making about the value of empire?
The person I'd point to as an example would be Frederick Lugard, the author of The Dual Mandate in British Tropical Africa. Lugard was one of those people that Robinson and Gallagher had in mind--after a tour of duty in British India, he more or less went to East Africa as a soldier of fortune, hoping to make his career--he wasn't ordered there. He got involved in a conflict in Uganda and ended up drawing the British government into it. This started his career as an imperial administrator, which continued in Nigeria. Lugard's book, published in the early 1920s, was his attempt to claim credit for the standardization of imperial authority--to be a kind of "operator's manual" for the British empire in sub-Saharan Africa. Some of that was humbug--he took credit for other people's actions, and was often describing what had already been done as if it was his recommendation for what should be done. But he still had a sizeable influence on imperial civil servants and on the British public--the book is also partially an argument against strong criticism of empire within England.
So how did someone like Lugard address decolonization? Well, this is one of the most interesting and perhaps representative things about his book: it is bursting with some really astonishing contradictions. (The conclusion of the book is the clearest example of this.) Lugard essentially says the following:
We're just ruling these places until the people who live there are ready to rule themselves; we're working to get them ready for self-rule while also not interfering in their cultures too much. (aka 'indirect rule') So here it seems he anticipates decolonization.
But you know, it's going to take so very very long that we might as well see imperialism as a permanent thing. Anybody demanding decolonization now is crazy. [Lugard very pointedly wouldn't even respond to literate Nigerians who frequently criticized him in independently published newspapers--to the point of not even acknowledging that such people existed]. And much of the book argues strenuously against any deliberate actions that would educate or prepare Africans for independence--this, he says, would interfere too much in their cultures.
Lest anyone in England think this is just altruism, guess what? It turns out that empire is completely vital for our own economy and national security. We British need the resources of Africa under our own direct control, developed for our own national interest, and only imperial government can do that.
So here using Lugard as a somewhat typical example of imperial logic, I think you can see how many government authorities (and the wider European publics) were able to simultaneously address decolonization as a future prospect and the supposed benefits of imperialism for their own countries at the same time. Basically, through a completely incoherent, twisted kind of contradictory logic that let them pretend to be moral actors at the same time they were more or less justifying theft and exploitation--and that allowed them to put their fingers in their ears and shout really loud any time literate, educated Africans tried to demand greater rights or to begin talking about decolonization. World War II is what made that contradiction unsustainable, though a great many British officials and members of the public kept trying to sustain it all the way into and even after decolonization was underway.
I'm not well versed enough to speak for every single colony specifically, but in general there was not plan for decolonization when the colonies were first made, and in many cases the colonizing powers fought tooth and nail to hold on only to abruptly give up and pull out at the end.
A fair amount of the push for decolonization stems from the Second World War. As part of the Atlantic Charter, FDR included a clause relating to autonomy of colonial holdings, and the heavy reliance on colonial troops inevitably led to many of them bringing home nationalistic ideals when they returned. Meanwhile, the economic damage done by the war left the colonial powers weak, and postwar dealings with Italian colonies in the Horn of Africa ended up setting precedents for the ideas of self-determination and independence of the colonies - Eritrea was handed off to Ethiopia, and the idea of breaking off Ogaden from Ethiopia into a Somali territory to provide a unified Somali state (although it was shot down by US pressure).
Britain in particular found itself buried in debt and heavily pressured by the US to grant its colonies autonomy after WW2, and only the threat of Communism really seemed to slow things down. The independence of India and Burma would come in 1947 following efforts that spanned into the pre-war era, although Britain would hold onto Malaya as it fought to fend off communist insurgents. However, a more conservative government would come to power following Indian independence, taking a more pro-colonial stance, and independence movements were somewhat stifled - Egypt and Sudan would gain independence in the '50s, but Britain was taking its time with decolonizing Sub-Saharan Africa, ostensibly under the guise of nation-building. The Gold Coast (now Ghana) would have enough unrest that Britain would grant them independence in 1957, making them the first Sub-Saharan African colony to become independent, followed by a wave of decolonizations in the '60s. The decolonization didn't always go smoothly, with Nigeria's in particular being criticized for creating an artificial nation out of three vastly different regions (ultimately leading to the Biafra War), and many white settlers weren't particularly happy with the process. Southern Rhodesia would unilaterally declare independence in 1965 with the intention of retaining its white minority rule government indefinitely, and along with South Africa they became international pariahs until they finally transitioned to majority rule at the end of a long period of unrest.
France, on the other hand, fought hard to retain its colonies in Indochina and Algeria, only to finally decide to cut their losses and decolonize. Algeria in particular was an interesting case, as France tried to incorporate it as a department of Metropolitan (European) France rather than a colony. Unfortunately I'm not very familiar with much of the specifics of French decolonization beyond that.
Belgium had no real plans to decolonize the Congo due to business interests up until 1959, when the decision was made with little preparation. The Congo was granted independence the very next year, and for a variety of reasons the country has been beset by unrest ever since.
Portugal was the last significant major colonial power in Africa. Like France, they tried to hold onto their colonies indefinitely, with the dictatorial Estado Novo regime trying to maintain Portugal's colonies under a similar guise to French Algeria. Holding on long after the rest of the continent was largely decolonized, Portugal became a pariah much like Rhodesia and South Africa up until 1974, when a revolution overthrew the Estado Novo regime and made the decision to rapidly decolonize. By that point, Portuguese Guinea was already independent in all but name thanks to a successful guerrilla movement, and much of Mozambique had also fallen to rebels. Ultimately, the decolonization process went about as rapidly as it did in the Congo, which had some disastrous results in the case of Angola, where the very short notice of independence saw three competing rebel groups (FNLA, MPLA, and UNITA) fighting over control of the capital while Cuba, Angola, and Zaire sent in troops to back their sides and the US, China, and the Soviets funneled in support for the sides they were backing.