Even if Doomy were on his best behaviour, I don't think the community would be generous enough to forgive or forget.
Heck, if Gandhi logged on as Doommaster he'd be swearing and arguing within 5 posts due to the inevitable baiting which would occur.
Whether Doomy has changed or not, there is no way he's going to be able to discuss and/or post in the same way as any other user would be able to. He just wouldn't receive the respect necessary to be able to have a meaningful discussion.
For the sake of Doomy, as well as everyone else, I would argue it would be a bad idea to reactivate (any of) his account(s).
Sorry Doomy.