How would a funeral home handle this?

What is done in the case if the deceased has been decapitated, missing limbs, completely mangled etc? Is there a way to fix the body in order to give an open casket at a visitation/funeral or would it be grounds for mandatory cremation or something like that? I know this is a strange and dark question but its always been one of those things I've been curious about and its something I've never had the nerve to ask because lets face it, this isn't exactly a pleasant topic and it can be unsettling to people. I've heard so many different stories about how this situation is handled so I'm just curious to know.