It depends. If the waiver neglects to mention they're using a vehicle that isn't certified, then to my non-legal mind the wavier immediately collapses.
Going on a trip like this is fraught with danger. It's natural to accept there is a risk of death, but it is the operator's job to minimise that risk. If they have played down the deficiencies of the machine, it's safety apparatus etc, then I'd say the surivivors or the families of the deceased (should it come to that) have a case that the travellers would not have signed the waiver if they had been made fully aware of the situation.
People do questionable stuff all the time. People often try to stay the night on Hilbre island for example, and often the coastguard have to come out and get them. That costs taxpayers money, mounting a rescue that shouldn't need to be made - because people took an unnecessary risk. Okay, the risk is marginal compared to diving on the Titanic, and they're doing it illegally. I'm just pointing out that you don't have to be a billionaire to consciously take unnecessary risks that can get you into a tight spot.
As I posted earlier, according to Mike Reiss, the waiver tells them three times on page one alone that they could die, and continually lists the ways you can die throughout the waiver and David Pogue of CBS says the waiver explicitly states that the vessel is not approved by any regulatory body. He also reckoned stuff like the lights were bought from an online hardware store.
How anybody thinks that going down to a depth of 13,000ft into the ocean in an unapproved vessel is a good idea, I'd never know. As I said earlier, it took me two minutes to find a company called Triton, which manufacturers proper submersibles, the BBC used a Triton 3000 to film programmes like Blue Planet II, Galapagos and other Attenborough shows, that's capable of going to over 3,000ft, then they have the 13000/2 Titanic, the model that has filmed the Titanic and is rated at over 14,000ft and they say that no matter what happens, it will return itself to the surface in an emergency. Every sub they build is certified by a third party. If you are going to do such extreme stuff as going down to the Titanic, you either do it properly, or you don't bother and you certainly don't do it in a cobbled together piece of shit.