As I have stated in other threads, MAD only works when the damage you can inflict is unacceptable to your opponent, and that opponent is sane ( enough to realize that).

There are a number of rather good fictional novels about the effects of a nuclear war- A Canticle for Leibowwitz, Level Seven, Alas Babylon... But fortunatly, we have no direct experience with it. I hope this remains so- but fear that there are those for whom the destruction of (Western) civilization would be desired.