... Share your opinion about the case, just asking. Thanks.
First of all, I'm not a lawyer, but have acted as an expert witness for several recreational and commercial diving deaths in a number of jurisdictions. As you have already received several good answers to your questions, I might just add:
1/ In civil litigation, much is dependent upon the jurisdiction and personal opinion of the Judge/Magistrate/Jury. In-fact, they are the one's whose opinion matters. Because of this, no one can predict the outcome of a case; however logical one conclusion may seem.
2/ The strength given to a liability waiver is also dependent on jurisdiction. Generally speaking, it often requires informed consent. This means that the waiver must be given based upon a clear appreciation and understanding of the facts, implications, and future consequences of an action. In other words, the person signing the waiver must be in possession of all relevant facts at the time consent is given.
So if we try to apply this, we first have to ask ourselves is it reasonable for a non-diver to be in possession of all the relevant facts of the extent of the risk diving entails? Just based on what I've seen, in the case of death having a liability waiver isn't reassuring.
3/ If an Instructor/Divemaster conforms to all certification agency requirements, that does nothing to release them from liability. For one Agency to state X is needed, doesn't excuse the Instructor from acting in a manner that is deemed reasonable under the circumstances by the Court. This is why various 'Experts' are used to establish the Duty and Standard of Care.