Assuming the terrorists get their bomb from North Korea it would be quite survivable for people a ways away from ground zero. A Hiroshima size bomb would have less impact on a concrete and brick city than it did on Japanese construction. If the Russians supplied a larger yield bomb, the kill zone would be much larger but the drill for survivors would be the same.
These people have to PREVENT such an attack. They must issue no more visas to FOREIGN Muslims. And intensify vigilance over foreign born and “home-grown†Muslims already here. The vigilance should be overt, heavy handed, and unashamed. Muslims are the problem.