All the advice I’ve seen on writing recommend that you develop a “back story” for your characters. The back story is what happens to the character right up until the story starts. This is very valuable to the writer when they create the character.
What occurred to me was that I never heard anyone talk about what I’d call a “post story” which is what happens to the character after the story ends. I suppose that some writers would think that a “post story” would be just a part of the “back story”, but I don’t recall that I ever saw anything along those lines.
It reminds me of the movie Backbeat about the early days of the Beatles. Part of the interest of films like this is that you know what happens to the characters after the story ends.
The story need not be a direct precursor to the “post story” or, for that matter, connected at all. Even though you may not share it with the audience, it would help you to have some idea what happens to your characters after the story ends.