I absolutely hate it when an author is asked a question about what happens his characters after the end of the book and he says something to the effect of “I’d like to think that they . . .”
Let’s step back from that for a minute and think about it. They are his characters; it is his story. The characters are figments of his imagination, and if he wants them to do something, then guess what? They have to do it. That’s the cool part about being an author: you are the absolute god over the world you create. Pretty spiffy.
The characters are not real, they don’t decide things, the author does. Your book might have been good, but it wasn’t so good that people actually began believing that your characters literally came to life.
Now maybe the author just doesn’t want to ruin it for the readers, wants to give them the option of finishing the story in their own minds. It’s a cop out, but I’ll accept it. Maybe he doesn’t want to risk making people dislike the story by adding more to it. That has happened to some (read: George Lucas).