[development] Implementing a user deletion policy

We ran into a problem involving deleted accounts, so I'm looking into implementing some tighter controls. However, it doesn't appear that user_delete() is a hook, so I can't intercept it. I suppose I can filter out the "delete" button, but are there any other obvious solutions? I don't want to kill any kittens. Also, Watchdog logs the deletion but not the ID of the user who deleted the account. Seems like an oversight.