You - a hypothetical film director and franchise creator - have made a franchise of films that have garnered praise from both critics and audiences. Your first two films are guaranteed modern classics, and now all you need to do is bring it all home with the third and final instalment.
Should be easy, right?
Surely you knew exactly how to handle this story the moment you started, and have never had to make any compromises whatsoever? That kind of interference never happens in Hollywood.
Starting a franchise is easy, and ending it is just as easy. But ending it in a way that satisfies everybody is damn near impossible.
You could have the best, most romantic ending in the history of cinema, but there will always be that one loveless son of an expletive who hates romance. But it's definitely not impossible.
Franchises have been around for a while now, and have only grown in number, so for your hypothetical ending to your hypothetical franchise, study these very real endings to amazing franchises, that managed to bring it all home and stick the landing.