I find it rather crazy that countries haven't done anything to North Korea before this time We knew from the beginning that they had been building nuclear weapons, and although they stopped (after repeated warnings) this should have indicated that they would do something in the future. They should have been punished for their actions long ago and not let it escalate to today's problems
I'd be really surprised if that happened. There would be too many implications of that happening, not to mention US can more than easily cope with it.
The last I heard, the longest range missile they had would fall about six or seven hundred miles short of Hawaii, but that doesn't necessarily mean they've managed to fit a nuclear warhead onto one yet even if they've pushed the range farther. But my info may be somewhat outdated.