PD is not a suitable model for MAD. It would be if a pre-emptive attack on an opponent would guarantee his utter destruction and eliminate a threat. But that's not the case - even in case of a carefully orchestrated attack, there is a great chance of rebuttal. Since military advantage of pre-emptive attack is not preferred over a lack of war, this game doesn't necessarily indicate to defect-defect scenario.

This could probably be better modeled with some form of iterated PD with number of iterations and values of outcomes based on decisions made along the game. Which I guess would be non-linear.