The stories told by Hiroshima and Nagasaki survivors are harrowing. If there was a nuclear war, whomever survived would also have to find food and stay alive in what would likely be a global nuclear winter that might last many years. Then the Earth would not be able to sustain life not just because of radiation, also because of endocrine disrupting chemicals which contaminated the soil from the burning of plastics in the tall buildings in cities, which contain huge amounts of it. Also their burning produces carbon nanotubes which make the immune system go haywire. Carbon nanotubes hygely complicated the health situations of the first responders who heroically responded to the terrorist attacks in New York on September 11, 2001.
So, multiple possibly insurmountable problems would face survivors. Another issue would be spent fuel in nuclear power plants. If society broke down, that spent fuel would not go away, instead it would - as it would if society did not break down but simply power for colling the cores and spent fuel was lost, a chain of events would occur that would leave the earth even more contaminated than it has been from the hours long nuclear war.
To grow food every bit of land would have to be laboriously scraped to remove the top few inches (the longer they waited the worse it would get) If they didn't do that human reproduction would be endangered, a substantial percentage of whomever was born would likely be deformed. Food would become insanely expensive, so much so that many of the surviving people would likely become food.
We have to stop doing things that are likely to cause serious problems for future generations to make money now. Endocrine disrupters are already a serious health problem due to our widespread use of them despite knowing their dangers since the 1930s. As much as 1.5% or more of the GNP in Europe is spent in paying for the health costs. Diseases like breast and prostate cancers, as well as neurological conditions and morbid obesity are theoriezed to be caused by their widespread presence in the environment and peoples bodies.
(The cost in the US is likely far higher because the US regulates them less, and has been using them longer, but its unknown because of lack of universally affordable health care.)
Its not widely known but EDCs cause morbid obesity by means of obesogens in numerous widely used products, things like nonstick cookware, flame retardants, food packaging liners, dental restorations, and many other chemicals people use daily. The epidemic of morbid obesity and metabolic syndrome, diabetes, etc. may be at least in part caused by EDCs.
The world doesn't have to have all these dramatic catastrophes to be endangered, simple greed and failure to protect society by acting responsibly is enough.