From a discussion on Burn Immediately.
SPOILER NOTE
This references material from the GM-Only section of In Dark Alleys and should not be read by players.
The purpose of most elements of modern society is to keep people distracted so they don’t find out any of the important truths. Thus the collapse of society after some apocalyptic event would be a bad thing for the powers-from-beyond, who would go about trying to rebuild society as quickly as possible. If there were any of the powers-that-be left, the p-f-b would give them a large amount of power (more than they would have deemed prudent in less challenging circumstances). This means, among other things, flooding the world with a lot of “holy” objects, and that the powers-that-be would start exposing naked supernatural power to the masses (rather than keeping things subtle). If none of the powers-that-be survived (which is certainly possible if whatever happened killed off a large portion of the population and there wasn’t enough warning to get into bomb shelters) then the powers-from-beyond would choose whoever is championing the rebuilding of society and make them the new powers-that-be. The problem here is that these people may not have the population to follow order blindly and may turn against the powers-from-beyond.
If an accident that kills a few hundred people, like a train crash, can create a new Survivor, then a massive global apocalypse could create many Survivors. Survivors may even outnumber regular people. Things may have gotten so backed up in the land of the dead that many human souls (ghosts) may have escaped back into this world or even into other worlds.
A massive population loss would cause many places to become abandoned, and so after a few decades one would find the ruins of cities full of Dances, and with many psychologically-damaged survivors wandering about there is no lack of people to be made into Faustians.
With the powers-that-be no longer able to actively suppress such movements, Scribblers, Cannibals, Animists and Androgynes may become large scale movements. A wanderer in the post-apocalyptic world may find entire cities based on these ideologies.
Another consequence of the powers-that-be losing much of their power is that a lot of hidden monsters might decide that they no longer need to keep themselves in check and only hunt those who won’t be missed. Instead, many monsters (especially Torturers, IDA p.233) would start openly hunting and attacking people whenever and wherever they please.
Then there’s the problem of souls. If most people had souls when the population of the world was nearly three billion, then what will the powers-from-beyond do with all those souls when the population drops to a matter of millions? One thing they could do is expand the land of the dead and let souls stay there longer. Yet souls cannot stay in that state indefinitely (if they could, there would be no need for this world), and doing this increases the chance of a soul becoming semi-awakened. The powers-from-beyond may start putting human souls in animals (this is something that occasionally happens by accident, but now it would be done on purpose), and one would find a lot more supernaturally-smart animals in the post-apocalyptic world, yet this is also not without consequences. Another possible strategy would be to purposefully put multiple souls in each human body. As we have seen, when one human body accidentally gets two souls (see IDA, p.238), and that second soul usually becomes a sort of super-powerful-psychodynamic, capable of occasionally taking over the person’s body entirely. What would happen if many souls were put in a single person? Would they take on the roles of psychodynamics, each more self-aware of what they are than any normal psychodynamic and each trying to take over the conscious body? Might there be people with no dominant personality but multiple personalities, each of which has its own soul?