We currently have no guidance for outdated questions, however, I strongly agree with Raven Branwen. Such questions shouldn't be hidden, because people may still be interested in and search for info on how certain things worked like in the past.
I'm also not fully convinced that closing questions is the right call here. When a question is closed, it's no longer accepting answers. Even though something is outdated or removed from the game, it doesn't mean that new information cannot be obtained or discovered, e.g. we learned a lot (and may still learn) about the gamemaster role after it was removed.
In my opinion, the best way forward for now would be to either edit outdated questions to include a warning or create a special-purpose tag that would serve as a warning (similar to the special-purpose tag for spoilers -
https://www.tibiaqa.com/tag/spoiler)