Sometimes accidents happen, and a mod might accidentally delete a comment too hastily, delete the wrong comment because chat moved, or just simply misclick on chat.

There's an option to unban, but not to undo deleting comments. The comments are still there and visible (if you're a mod, or using the BTTV extension) so there must be a way to un-delete comments when mods make a mistake.

Being able to undo that mistake would help prevent the mod and the person whose comment was deleted feel bad about the situation, especially because ALL the person's previous comments get purged from chat and the VOD.