North Korea doesn't have the technology to do this. They don't have a reliable vehicle that can get here, and they can't yet put a nuclear tip on a missile anyway.
At this time there is virtually no chance your scenario could play out.
This is almost certainly just more bluster. North Korea is just trying to raise the temperature and sense of crisis, and in a few weeks they will claim the US and South Korea backed down. It's how this criminal government does internal politics.
If they can put a satellite into orbit they can put a plutonium bomb into orbit. Plutonium bombs weigh a lot less the Uranium bombs.
This prof of astronautics says North Korea’s December 2012 ICBM satellite launch was more advanced than the media and US gov’t sources are saying. Watch his video starting around the 15:00 minutes mark.
“Professor of Astronautics Mike Gruntman uses principles of ASTE 520 Spacecraft Design to look at the North Korea satellite launch on December 12, 2012.”
Video: http://vimeo.com/60007637