Board Thread:General Discussion/@comment-26951903-20151022170042/@comment-1757994-20151022203532

If they are globally banned, there's not much reason to keep their User: and User_talk: pages. (Remember to check WhatLinksHere, of course.) If they're not globally banned, but either locally banned or just voluntarily left, it's up to the individual wikis' policies and the users' requests. IMO it would be good to keep/archive any talk pages, at least.