I like the analogy with the prisoner's dilemma, although I think the situation is slightly different. It'd be like playing the game against someone who's repeatedly shown that he'll betray you whenever possible. The optimal strategy in that case is not cooperation.
As for the civilization is dying thing, I'm not prescient, so I can't give a clever answer. But even if it is so, that has no impact on what the optimal behavior is for someone purely selfish. Like good king Louis XV used to say, while bankrupting the kingdom of France: "After Me, the Flood".
