I don’t understand why you think there would be any ashes? Extreme population decline like the Black Plague or WW2 caused extreme wealth. Slow decline will cause a slow increase in wealth in the following generations. If we have half the people we only need half the goods manufactured which means half the people is fine. We had only 4 Billion people in 1980. It wasn’t a post apocalypse hellscape. So if we returned to 4 billion it would be fine.
The only people who suffer from population decline whether it was the Plague or great wars are the wealthy because their livelihood comes from skimming a little from all the workers.