Thanks a lot. RobinZ sent me the paper and I read it. The key part is indeed the definition of the disagreement point, and the reasoning used to justify it is plausible. The only sticky issue is that the disagreement point defined in the paper is unattainable; I'm not sure what to think about that, and not sure whether the disagreement point must be "fair" with respect to the players.

The "common priors" property used in the paper gave me the idea that optimal play can arise via Aumann agreement, which in turn can emerge from individually rational behavior! This is really interesting and I'll have to think about it.