i've not read the book, but i've thought about this on and off for a while.

the common trope of a mad max style wasteland where there are roaming barbarians and everyone is in a state of disorganized chaos is imo overstated. a hobbesian fantasy/wet dream.

humans tend to be self organizing and (mostly) altruistic in the face of disaster. we have plenty examples of this: fukishima, the boston bombing, ongoing ukrainian conflict, syrian conflict.

that's not to say that scoundrels do not exist. times of chaos create space for predators to take advantage of people. it happens more frequently at greater scale. there will be plenty of untethered folks with some form of military training.

similarly, the idea that you could simply ride out a long term disaster in a prepper cave is (again coached in an imho) mostly a fantasy. most people simply need community to survive.

fear of warlord run gangs shouldn't dissuade you from having a small stockpile of goods to survive. if they exist, and you meet they'll probably chop your head off regardless.

the most sensible thing to do is prepare within reason and build a community of people around you that can rely on you and vice verse.