Liability waiver are not the end all, be all of legal action. If the company was negligent that is not going to be covered in the waiver. There are also other caveats that may be relevant to if the waiver is valid and enforceable. I'd be curious about which jusisdiction's laws apply.

Not only can you absolutely argue with a waiver (and I'm sure the families will), but that's only an agreement between the company and the customer, not the customer and the governmental agencies involved in the rescue.