Why not create a hack that back's up users and all their info?
...wait, already created just use the backup--d'oh
But still, if you made something that allowed users maybe in their profile to select an option that allowed, incase anything happened to their account, it could be backed up. Then there could be some nifty interface in the admin area that contains all users who were deleted and who choosed to have a backup, and all their backups are located there. Where the admin can choose to backup/restore a user to the point before deletion, or just delete / mass purge back ups. In order for it to be a recent backup, all that would need to be done is right before the user deletes themself or admin deletes user, a backup is created (if the user choosed to have a backup). The difference from this and the regular backup Sql dump, is that its easier (with an interface), and that not everything is needed to be backed up (although I'm aware the other way you can do the same, but this is more organized..i think)
YOU know what I mean?!?
Damn..I'm getting way into this, and it probably wouldn't even work...but, maybe If it did, I just created a hack I could possible do?!? .....nah, I'm not that great at php/mysql yet to accomplish such a huge task. *eagerly awaits response by Firefly*