Yep, very funny Dan: but seriously. What they're required to do is no more than everything "within the law and their code of professional practice", or equivalent lawyer's fudge. Surely ending the world is not within the law, or permitted by any code of professional practice?
Um, well, I think we might have a loophole here, big enough that we won't even need that bloke who gets celebrities off speeding offences. So long as the law permits drilling holes into a methane swamp and super-heating the atmosphere, the fact that it's manifestly catastrophic to do so is neither here nor there. The worst they'll get is corporate manslaughter of everyone on the planet, and in any case they'll probably call it an act of God, before attempting to call Him as a character witness. It's the biggest loophole in the history of law.
One silver lining: their responsibility to shareholders is to maximise profit in the long term, so they can still be found negligent if, by ending the world, they shorten the term over which profits can be earned. Thing is, at the current rate of political progress, Cancun notwithstanding, only Doctor Who will be in a position to haul them up for it.