John:
I've been absent from the board from a while, but yours is the first post I read when I logged on yesterday. Your hypothetical is actually a bit more complicated than you probably intended.
First, Cozumel is in Mexico. Mexico's tort law is positively paleolithic compared to U.S. tort law. Mexican torts come directly from the Napoleonic Code of 1804, and those sections of the Civil Code haven't been updated in two centuries. And the jurists who penned those code sections didn't have a high opinion of common law torts espoused by Britain and its possessions.
Tort liability in Mexico is largely based upon contract. If a person fails to undertake an obligation imposed under a contract, then liability may arise. For instance, if the operator agreed to conduct a dive and someone got hurt, liability would arise under the contract for that injury.
Mexico also has a concept of "objective liability" which is akin to strict liability in the U.S., but its application is fairly limited and would not reach this situation.
A third concept is "extra-contractual liability." This area of law is extraordinarily undeveloped in Mexico and the code sections relating to it are scant. This is the area where one might find negligence (as a U.S. attorney understands it), but exactly what it is an how it is implemented is largely a mystery. Tort practice is essentially non-existent in Mexico. The majority of firms do not accept tort cases (some boast that they've never accepted a tort case).
Moreover, any sort of contributory negligence on behalf of the victim is a complete bar to recovery under Mexican law. So doing something stupid (like chasing your buddy beyond certification limits) could prevent recovery. Interestingly, Quintana Roo is the only state that has not adopted the Federal Civil Code's contributory negligence bar. However, if the diver booked the excursion through a U.S. entity rather than a Mexican entity, an exception applies to the case and the Federal Civil Code governs the issue.
Bizarre, wot?
Also, tort recoveries are pitifully low in Mexico. They're based on a factor of the minimum wage in effect on the date of the accident, multiplied by four, then multiplied by the number of days the injury exists. There is no "pain and suffering" recovery or punitive damages, which is where you see the really large awards in the U.S.
Assuming that Bob and Jill came back to the U.S. and Jill sues Bob, we may (or may not) have a different result. The first question is, did Bob owe a duty of care to follow the dive plan? The question of duty turns on whether a consequence of an action is foreseeable (which is an odd standard by itself). So was it foreseeable that Jill would follow Bob to 250 feet? Jill is trained not to go below 130 feet. But she is also trained to stick with her buddy. That's a hard call. I think that any expert witness put on the stand would say that every recreational agency would train Jill not to follow a buddy below 130. So no, Jill's following Bob down was not a foreseeable event. If the event was not foreseeable, Bob owed no duty to Jill, and Jill loses on summary judgment.
The only reported case of which I am aware involving the duty of a buddy is Rasumussen v. Bendotti. I've discussed it at length in other posts on this board. In that case, the duty owed to a buddy extends at least to the conduct of pre-dive safety checks, but the duty to a buddy can be superseded by a personal emergency. So under Rasmussen, it's o.k. to leave a buddy if you have a problem.
On the intentional tort case against Bob, I think Jill would have to demonstrate that Bob knew Jill would unavoidably respond in a particular way when he bounced to 250, took actions calculated to produce her response, and that injuries resulted only because of Bob's actions. Jill would have to prove that Bob is one seriously evil bastard, and that her free will was terminated or suspended as a result of his actions. I don't see it happening, but I'm just making up this analysis based on what I know about intentional torts (which isn't a whole lot).
Of course, Bob could argue that even if he did disregard the plan, both the DM and Jill assumed the risk of a known possible injury when they followed him down, and that would insulate him from liability.
This is probably an unsatisfying discussion, but it's an odd hypothetical.
