I understand that we have to keep historical information of users, in fact I need this. I was just hoping that the re-registration would work because your solution above will not carry over all the user's historical data. Maybe there should also be a re-activate option (allong with ban, delete, require verification, etc) for admins so we can control deleted users who keep trying to re-register.
BTW, a strange behavior, if a user is deleted, and he tries to re-register, he gets access to the system again after registration. If he was not taken off group memberships which allow permissions, he is able to access those modules. But when he logs out and in again, he is again prompted to register.
anyway, thanks again.