His "great pains" didn't pay off, IMO. The piece-meal cannibalism, for example, doesn't ring true. We don't cut off cows' legs one at a time, right? Never did, even when people slaughtered animals on family farms. Bandits don't randomly walk down roads, they set up ambushes.
IMO, it's a poor entre into the disaster novel genre. It was done better in Earth Abides
, with many of the same themes. Niven and Pournelle did it better in Lucifer's Hammer
, with many of the same themes, including cannibalism.
plots are a construct of fiction
And this is fiction. A plot provides the framework upon which you hang your philosophy. He could have written an essay, and done a better job of getting his meaning across.