I have been guilty of this is in the past. A while back I pruned my photobucket account and plum forgot that some of the images were linked to websites. Folks got red "X" instead of a pic. The other issue is if ya go to your account and edit an image for any reason, and don't save it as a copy, you've changed the address of the original, so in effect it's gone too.
Nowadays I edit a copy, and never throw any pics out. Photobucket has huge storage limits, so it's not really a problem.