When we jump to season 6 we're going to be deleting all the old incompleted/dead threads, inactive characters, requests, etc. There will be an archive for all the threads that were completed, we're not getting rid of those.
That being said if you want to keep anything, any old characters that you created and retired, any old posts from inactive threads, etc, you need to back them up now. Once we do the jump they will be deleted. So gets to backing up whatever you want to (that is yours to back up) and we'll take care of the rest.