What we don't really understand is the lethality of the second and third order effects. People who can't be fed (because industry has collapsed) don't just sit

What we don't really understand is the lethality of the second and third order effects. People who can't be fed (because industry has collapsed) don't just sit and die peacefully. Foraging is unlikely to work, since our natural ecosystems are not large enough to support large-ish human populations and would soon be destroyed by overuse (damage to them from the actual nuclear war being beside the point). A huge immigration crisis in the rest of the world could have its own highly disastrous consequences. Finally, I wonder how bad the effects on reproductive health would be from the various radiation effects be? Humans who had trouble reproducing, with a much degraded medical system might face further downstream problems from that. Same thing with animal species, which might cause more food troubles. Point is, there is significant survival trouble just from a violent collapse of civilisation, that estimating the probability of human survival is fairly impossible. Finally, if humanity becomes so critically weakened, even (by today's standards) minor disasters might become extinction events.