NYC is already that dense, and much of Asia is even denser, and those epidemics haven't wiped out populations yet. Part of the assumption (mine, at least) is t

NYC is already that dense, and much of Asia is even denser, and those epidemics haven't wiped out populations yet. Part of the assumption (mine, at least) is that we're talking about NYC-quality infrastructure too: water, waste management, health management, law enforcement, emergency services, etc. The megacity would have the resources and facilities to identify a disease like that as soon as cases started to show up, and contain and treat the problem before it got out of control. Those diseases would also be less likely to show up in the first place because of better living conditions for everyone. Here's a drawback: what would everyone do for a living? NYC doesn't have much manufacturing anymore, and industry like that takes up space. It would have to be outside the city, and people working for manufacturing industries would have to live near the factories. Farmers would live outside too, as I mentioned before. Fishermen too. There's probably a bunch of other activities that would require people to live outside the city, so not everyone would be a city dweller. Probably a good 80%+ would be able to stay in the city though.