The way I see it, when someone comments, the notification is generated immediately, but never updated. Only the author or imgflip mods can delete a meme. But reporting a link to imgflip could potentially get something deleted. I don’t think text comments can be accessed on a deleted meme, but meme comments have a life of their own - they are stored in the users images and they are public, but you would need to know the direct URL to see them.