Shoutbox

The original scheme wouldn't work; I can see this happening;
User deletes thread > Moderator restores it > User deletes it again > Moderator restores it > User deletes it > Moderator bans the user for 24 hours and restores the thread.

Allowing users to delete their threads is a bad idea, always has been. M_E's idea of disabling the ability of users to delete threads, and just reporting it to a member of staff is a good idea.