[Dave]

You can't restore a deleted user, when you delete a user using the admincp it's physically deleting the user from the database.

However, I believe the username of the user is still present in the post table? Need someone to confirm this to me, if I'm right then your option would be this: create a new user and write down the userid. Execute an UPDATE query in the post table to set the userid of the entries with the new userid where the userid is 0 and the username is the old username.