By chance, do you have a backup of your public address book? I make a separate local copy of the public address book once a month for just this purpose. If I need to restore a user I can copy his/her Person doc from the local copy back into the current server copy. Then all I have to do is re-add them to the Groups they were a member of and I'm set.
If you keep backups of the ID files as well you can restore their ID file to them also.
If you can't go to backup, then recreate the user without setting up his/her email file. Next, manually re-add the user to the ACL of the old email file and make sure the Person doc in the public address book points to the right mail server and file location.
DDickey