In short, the treaty had few formal end conditions, but wasn't intended to last forever. To be more specific, there were plenty of dates marked for economic, administrative, and occupational purposes, but very few which concerned the military. Instead, the treaty's decommissioning was more informal, and would depend on the political realities of a later date. I'm only going to tackle the Treaty of Versailles signed by Germany, rather than the other treaties of the larger Versailles Conference.

Firstly, let's see what end dates the treaty did have. A large part of the dates were related to reparations; finance does love its formalized payment plans. Reparations were the most complicated topic, and most of the details were delegated to a later conference devoted specifically to the issue. The crux of the end dates was that all reparations had to be delivered within 30 years of the treaty. Curiously, there were also provisions concerning alternative forms of payments: the Germans could pay the bill in chemicals and dyes until 1925! They also could not export any gold without permission of the Allies, since it was all earmarked for reparations. One of the reasons this timeline was so well sketched was that there was a clear goal: repay the destruction caused to French and Belgian agriculture and industry by wartime occupation. Many other treaties, such as Brest-Litovsk or the Treaty of Frankfurt which ended the Franco-Prussian War, used reparations as a punitive measure. Certainly the reparations of Versailles were punitive, but on their face they were restorative. As we will see, the other aims of the treaty were less clearly defined.

There were also economic concessions and administrative deadlines. Certain goods like coal and chemical goods were required to be regularly delivered to aggrieved nations for 3-10 years, depending on the good. Other concessions, like the building and use of railroads and riverways, and fishing rights in the North Sea, were granted to aggrieved and new nations for (generally) 5 years. Administratively, deadlines were set for former German nationals in newly annexed territory to apply for German nationality (2 years), and for specific regions (the Saar Basin, Upper Silesia, and Schleswig) to hold plebiscites on whether to be German after 15 years.

The most relevant dates, or lack thereof, are about the German military. Parts of the Rhineland would be occupied for 5-15 years. There were also time-bounded limitations on the replacement of sea vessels, and significant control of German airspace and infrastructure was handed to the Allies for some years after, but that's really it. The ban on an air force, the demilitarization of the Rhineland, and the 100 000 man cap on the army all lacked end dates. Unlike French industry which could be built back up then called "Done" a German military would always be a threat if it was strong.

The mindset of the peacemakers is a trickier subject, and is more complicated than just going "Ctrl + F" for end dates in the Treaty of Versailles. By and large, however, the men at the table understood the world was rapidly changing, and the Treaty was not to be doctrine for centuries. The easiest example to point to is US President Woodrow Wilson. He famously expected the peace to build the foundation for a "New World Order", and wanted Germany to take its place in time among the other nations of the world. Germany, and every other nation, was expected to conduct its own negotiations with other nations. Countries both new and old were to carve out their place diplomatically, and having big armies running around would tempt leaders to use them. Therefore the parts of the treaty with unspecified end dates were less about holding Germany to the same standards a century later than creating the conditions for a new world to flourish. In a sense, the treaty wanted to make its own terms obsolete, because who would need a big army if you can achieve all your goals via diplomacy?

Contrarily, the Europeans (and especially the French) had a real hankering for justice. Many Frenchmen wanted Germany smashed so hard that it would never rise again, with a few radical plans even proposing the dissolution of Germany back to a pre - 1870 state. There were certainly those who wanted the treaty to last in perpetuity; but these were not the men in charge. Georges Clemenceau was something of a moderate, and held back a great deal of revanchism. He was still pulled by public opinion, but he diminished the effects of the French id.

The hamstringing of Germany was also a double-edged sword. Just on the other side of Berlin was a newly animated communist Russia, grinding its way through a civil war with an increasingly effective Red Army. The idea of the Bolshevik virus spreading to Germany cast a shadow over the peacemakers, and the Allies wanted to make sure Germany could defend itself (or at least keep France off the menu). Even as negations took place there were two major attempted communist takeovers in Germany, and another successful one in Hungary that was only put down after Romanian intervention. The Allies didn't want to be constantly bailing out liberal(-ish) regimes and expose themselves to threats. Therefore a delicate balance had to be maintained: Germany's economy and military had to remain docile in the face of the Allies, but stand as a stable breakwater against Bolshevism. In this regard the Versailles treaty was a document of a specific time and place, and I'm sure that in a communist Germany alt-history the rollout of the treaty would have gone very differently.

In summation, the permanency of the Treaty of Versailles was mixed. In finance and industry there were clear goals that could be achieved with a timeline to match, but the role of the military in a new German Republic was tied inexorably to situational politics. In the view of both Wilsonian idealism and European realpolitik the treaty was effectively in force "until further notice", with different actors having different views on when exactly further notice was due to be given. The concrete details therefore were a mix of public revanchism, security anxieties, and the reality on the ground in contested areas.