Regarding the support thread,
Undo should be a basic usability feature in case of date deletion. Like the trash box for posts and undo for gmail deletes.
* Can there be a backup comments feature? You can move the comments to another backup table and provide an option to completely remove that too later.
* If the above is not possible, could you please give a red big warning asking admins to verify that they are in the right site and make sure they really need to delete all comments? It should be made clear data is lost for ever.