Even with more powerful bombs, unless they're infinitely powerful there's going to be an area of total devastation, an area that's effectively untouched (by the blast, at least...radiation is a different matter), and an area in between where the destruction declines on a gradient from total to imperceptible. For more powerful weapons the fringe area may be pushed farther back, but still it's there--there's not a cutoff between "it's hopeless" and "nothing to worry about," that's just not how energy dissipation works.