It can be at any point during their fictional timeline, any way you want. Incidentally, are there any characters who were killed off that you wish weren't? For the latter, I would say "L Lawliet" and "Bruce Wayne". For the former, I'd want to see "Kitty" from the Bartimaeus Trilogy killed off. Yes, I know Bruce Wayne technically isn't dead, but he shouldn't have "died" in the first place. Also, I wish Jason Todd had stayed dead. Plus, I wish all the people in "High School Musical" and "Hannah Montana" were shot with a Tommy gun. And the HSM people burned afterwords.