by Christian Herman.
As far as I've been able to determine from a few minutes of searching through moodle.org, not easily. You would have to edit the user record int he database manually to reinstate the user and remove date stamps added to the username, email, and password. That would give the user access to their old infomation and activity. They would not be able to self-re-register. Even with this manual method, I'm not sure what would happen if another user had registered with the same username as the deleted user; that is, I'm not sure if the old user activity would link to the new username you would have to give to the old user.