20 Things You Didn't Know About Serenity
19. Characters Were Killed Off Because They Couldn’t Commit To A Sequel
Whedon successfully manages to get all nine main actors to return for the film continuation, however, some couldn’t return for a sequel.
Therefore, in his final script, Whedon had to kill off the characters of Wash and Book - played by Alan Tudyk and Ron Glass, respectively - as they couldn’t commit for future sequels. In the original draft, Wash and Book both survived, and Wash and his wife Zoe actually went on to have children.
Whedon has said, however, that Wash and Book could have been brought back in the proposed sequels, and he would make sure it would be in a way that “audiences would believe”.