Re: City Killer - Only you can destroy Philadelphia
I'll just throw things out there in order to throw them out there...
•After of the erasure, what is there?
A hemispherical crater in the ground filled with water. You have to figure the radius impacted would not me a circle but rather a sphere, so things above and below would be impacted. It sits on a river, and thus the water filled in. The new city might be floating, what with the massive effort it would take to bring in that much dirt. (I'm guessing "erased" part is actualy floating in another dimension, a la Marvel's Asgard.)
•Is it logical that all business shifts to Camden and then shifts back once the city is rebuilt?
Logic? What kind of game are you running! Actually I think that business shifts for the obvious reasons: Nothing's there, then it comes back because the infrastructure of the new city way outclasses the city that had taken over. Plus the government would offer inducements, like what they sometimes call "Hub zones". Basically if an area is underutilized, the gov gives tax breaks or lessened oversight rules to businesses to open up shop in that area.
Heck, that last bit might work for your Distopia. When the Utopia opens, business shifts to the shiney new city. The abandoned areas become under-utilized and so to boost them, rules are stripped away. It becomes a crime hub.
•Who rebuilds Philadelphia?
The usual suspects. Rich benefactors (Bruce Wayne/Tony Stark types), the state, and the federal government. But there's usually a person who is the rallying point. In the real world this would be a philanthropist or a politician who knew how to make it look like it was all his/her doing.