They'd better have a way to neutralize what would be (if humanity died in such numbers) an omnipresent smell of death. If 18th century people could smell decay coming from the cage of gibbets (and they could) what do you think the odor would be from heaps of corpses unburied or uncremated in places where the living were not enough to attend to them? I harp on this but, still, no one else seems to even think about it. Why not?