Well, I admit to finding the idea of an entire community dedicate to the concept of poly extremely interesting, I don't think that a poly community would survive the end of the world any better than any other kind. In fact they might do worse because in severe survival situations, strong family units are often the key to rebuilding a civilization. And if you have 3 wives and 8 kids and all your wives have 2 or 3 husbands... well... it gets hard to know who to feed first when there isn't enough to go around.
With all my heart I will love and not fail,
With all my soul I will fly and not fall.