Would it be possible to leave up old scenario forums?
I think they are hanging around on the system anyway, and space shouldn't be that much of an issue. It would be good to have them for many reasons. One is that people who haven't participated yet in scenarios can see what it was like. Another is that it is sometimes fun or useful to go back and read about an old scenario.
If the BB admins are wary of clutter, perhaps they can all be put into their own category of forums called "previous scenarios" or the like.