The minute N Korea launches anything, that country will be wiped off the map within a few mins.
They launch, it would be immediate suicide!
they won't detonate a nuclear warhead over NK, since China would get the nuclear fallout. In the best case scenario, you will wake up and US fighters will be turning NK into powder while China sits on the curve. I'm guessing behind close doors the USA will give China some privileges to Taiwen, which they have been after for ages. But at some point they will have to overthrow the Klown King of Korea.
In modern times, the USA can go after Banana Republic leaders (Castro and Chavez), but do they have the balls to get in a multi-year jungle fight with another Asian country? They won't get the option to bomb troops in a flat desert like Iraq, will have to go into the jungles and veggies of NK like Vietnam. That's a serious body count on the American end.