Well humans can only survive if they coorporate and cooperation is built into our nature.
We would still do that, just in smaller groups than today.
That's where we came from, so it's what we will fall back to again.
The visions of marauding bikers from Mad Max are unlikely. That's only what you get if you have an all male youth group with no connections to anyone else.
But a mixed group would behave more like a traditional tribe.
Possibly very hostile to outsiders, but not quite as crazy on the inside, as the common horde of wasteland inhabitants you see in those movies.
