The minimum is 2 endings, each route must have an end. If you want to extend the story further you can create more routes with their endings. The idea is that your project is solid and complete.
the routes can be influenced later in the story, and that is what is important. for example, a bad decision can lead to something bad happening to some character, and that leads to the end of that route.
so the player must influence what happens in the game, and must be encouraged to choose which path to take.
I hope this solves your doubt, if you have more questions I will try to answer them.
