Dropping a character... Hey, it happens. You lose a character's "voice," don't have the time or energy to play them, etc. I'm sure everyone's been there at one point or another, so whatever your reason, you're welcome to drop your character(s) at any time.
If you wish to play a dropped [canon] character, that's cool, too. Keep the change natural, though. If the previous player's final post as that character included him or her attacking someone, don't make your next post ignoring that encounter entirely.
If you're going to drop a character, please leave the following in a comment. All comments will be screened.