It's modern day, shortly after a devastating war. Similar to Kowloon Walled City in China, both countries involved with the city don't want to care for it and leave it to its own devices. However, this war left the city wrecked beyond belief and killed the majority of its inhabitants.
People don't leave it for several reasons: The city is all they've ever known, they wouldn't know where to go, they believe they can rebuild the city, they think it's too hard to leave, the typical stuff.
People in the city believe the world has ended and eventually divide themselves in to small communities.
They can't call or text or email or use a computer at all.
The real kicker is that the country in which it's located (US of A) doesn't care to ensure the population's survival or it's too dangerous to check on the people(for 27 years, in case you need to know).
So I'm trying to figure what exactly would cause the US to abandon the city for 27 years from 2016 to 2043
Other information: It's a port city, located in Maine, that became popular during the civil war, transporting supplies to the Union Army from traitors on the Confederate side. During this time, Russia also occupied the city for a while, protecting it from a possible British invasion.
The city doesn't have regular power throughout the city, but renewable energy generators are used when available. These don't power the whole city and, at max, a local grocery store.
All of the stuff with Russia happened during the Civil War and is no longer relevant; it's more of a history lesson. As far as dead bodies go, I would imagine that the people in the city continued by burying them, in mass graves at least.