I'm not sure what to say. If you don't have a valid email, there's no way to securing send you the link to register your password with the new forum. If you have a better idea, I'm more than happy to listen. If a user hasn't been using their account on the forum for a long time... well chances are they haven't been using the site much either. Either way, they can always just make a new account.
What about the activity, trust, posts etc... the user has earned? Would it move from old account to new account if user provide a signed message? But wouldn't it make this worst?
-MZ