While I hate that they did that, I don't think anyone was screwed by the lack of a Forrest Gump movie sequel.

The book is a kind of a mess, just more of the same adventures but worse and even more contrived. At best the movie sequel would have been forgettable, but there's a good chance it would just been terrible and felt like a parody of the original. I will say that Forrest creating New Coke was a good idea, that's the kind of thing that would have fit well into a movie.