I enjoy prognostication so please indulge me...
As for the opening campaigns of WWIII and the current imbroglio between Israel and Syria with poor Lebanon being ripped to shreds between them: the US will definitely survive this round.
If Iran does manage a bomb and indeed throws in behind Syria or if the Pakis ever go over to the darkside (they already have a bomb) I don't think I'd take a long-term bet on the safety of NYC. Its the most tempting target if they only have a couple. They'll pop one in Gotham, evaluate the effect and reaction and save the others...kinda like we did during WWII.
London is physically closer so it could get smoked instead of NYC if they are unable to make the Atlantic crossing,
On a brighter note, the vast majority of the US population will ride this out. Oceans are our friend. That said, life will get pretty sucky. Not necessarily Mad Max-style sucky, but a lot of stuff we enjoy will probably be curtailed or cease.
The sheer numbers of people who will need resettlement in the NY-NJ area the wake of a nuke blast in NYC would make the Katrina dealio look like small beans.
Of greater concern will be the casualties we take finishing the job in the coming years. I expect there are an awful lot of American 10 year old boys now in front of Xboxes who will get trigger time for real before its all said and done.
Another issue is what this will ultimately do to the economy. The stock portfolio would be in for a considerable hit if NYC is smoked, though those with a lot of liquidity could make a killing in the depressed market.
Then again, speculators always find a way to make money in wartime.
Hold on tight. It promises to be a very interesting couple of decades.