To answer your question: yes... kind of. It was one of many components in a perfect storm that all contributed to the end of fascism in Spain and the implementation of their democratic constitution in 1978.

Blanco never had a chance of replacing Franco. Spain had already fought a war with Franco and half the country did not support him, they were waiting for their moment and Franco's death set it off.

As Spain became the last fascist nation in Western Europe it was becoming more and more difficult to implement fascism in that era. There had already been numerous bloody labor strikes and protests since the "end" of the civil war, the people had been demanding change. So with the death of Franco went the death of fascism, and essentially, the end of fascist leadership... and the end of Blanco.

Its been years since I've read deeply into Francoist Spain, so I'm going to use my memory of historical events along with my current understanding of authoritarianism.

My opinion is that the roots to the democratisation of Francoist Spain took place during Franco's regime in the first place. Let's look back to the Spanish civil war. Franco's victory was due to aid by Hitler and Mussolini. During WWII and its immediate aftermath, Spain was looked on as an international pariah due to their close ties with other fascist regimes. Franco adopted an isolationist economic model, and strove to gain self-sufficiency, particularly in armaments, as the nationalists feared an allied invasion. During this time, Spain recorded negative economic growth, and was already at pre-civil war levels in 1939.

However, in 1951, as the factions of the cold war became apparent, Franco started to negotiate ties with the USA, allowing the establishment of American military bases in return for economic aid. At this point, Franco's economic policy also shifted towards a free market, making the country dependent on American aid and European goods. In turn, after various IMF loans, Spain's economy started to grow almost as fast as Japan's, leading to the term 'the Spanish miracle'. The Falange economic model was based on nationalist syndicalism. However, as the technocrats grew in favour, this resulted in a shift to an economy resembling a free market.

Another important factor is that although Franco's initial government was fascist, it was certainly not totalitarian. By the early 1950's, it devolved to a typical authoritarian dictatorship supported by the West. The Falange, although referring themselves as a 'national movement', functioned as a de facto political party under a single party system. As Spain's ties to the west continued to grow stronger, so did his authoritarian policies wane. For example, Franco had initially banned the public use of all minority languages (despite himself being Galician), but this was rarely enforced by the late 50's, apart from official documents. Another was his initial attempt to control cultural practices - flamenco and bull fighting were considered Spanish, most others were considered foreign and banned - this too was hardly enforced later on.

There were many other factors of liberalisation that occurred during the last years of Franco's rule. For example, women were not allowed to become judges and testify in trials. Nor could they become university professors. This was completely overturned after Franco's death, with some liberalisation taking place during his final years.

Another factor is that despite the end of the civil war, opposition groups such as the PSOE and the Communists continued to function underground in Spanish territory. While Francoist Spain was authoritarian, like I mentioned earlier, it was not totalitarian. While some leaders of the PSOE were executed, other were exiled or arrested. Opposition to the Francoist regime did function underground in a clandestine manner. In totalitarian regimes, suspected opposition members (and their family members/friends) were almost always executed or sent to labour camps (such as Gulags and Laogai). This did not happen in Franco's regime. While he was a dictator, and he did consider himself a guardian of the church, he was not particularly cruel unlike Stalin, Mao, or Hitler. The atrocities committed under his regime were mainly war time atrocities, unlike the massive purges and executions in totalitarian states.

TL;DR: While Franco was a dictator, he did not control a totalitarian state, nor did he have the apparatus or intention to do so. Liberalisation policies in the last two decades of his reign set the stage open for Spain's democratisation. Blanco's assasination was the last step for this shift.

Follow up: what was the role of the King of Spain in returning Spain to democracy? I've heard that the Juan Carlos is considered of highly because of his desire to dismantle the Franco regime.

Yes and no. Let me explain. Also, English is not my first language so I say sorry for any mistake and if you want me to explain something further, just tell me.

First of all, to stick to the question, did the assassinationn facilitate the transition? The most common idea is that, at least, it made it quicker.

Spain, in 1973, was directed towards a democratic governement. There was a huge amount of the populationn who was reclaiming a democracy, and even those who were inclined towards the right-wing knew that the dictatorship would end with the death of Franco.

The worst thing for the regime with Blanco's death was that there was no other 'solid' president for the country. Blanco was the very right hand of Franco, had the same political views (right-wing fascist, catholic, falangist, and opposed to any democratic aperturism). There was no other important political figure like that in the regime, because even the most important potilical figures knew that the country was requesting a change.

So, even if Blanco survived and were to rule the country, Spain was going to change to a democracy sooner or later. Just a little fact: beetween January and March 1976, there were ~18,000 strikes in Spain, a country with around 35 million people. That makes 20 strikes each day.

In the other hand; "death of Franco = start of democracy". Yes, it was very accepted, even in those ruling the country, that once Franco died Spain was going to change to a democracy. The question was "how".

edit; typo