Lets bear in mind Kim Jong Un is not quite the same as Kim Jong Il. Anyone whom things executing someone with a flamethrower or an Anti Aircraft gun has some pretty unusual views on leadership. Or maybe he is just a big fan of Dr Evil.
Not saying this is the time, but I think its inevitable things are going to go wrong sooner or later.
I'm not so sure actually because it'll go down when the big powers are in the mood to go in as well. A US led attempt to occupy North Korea will result in Chinese intervention just like in the last one.
This is probably another reason why South Korea seems to push back Japan and the US sometimes and tries to cozy up with China sometimes. If the Koreas ever unite by none war means, it needs to be on terms that both China and the US will be fine with. So if South Korea was more friendly with China, then China would find the idea of a united Korea under the South Korean government less repulsive. Russia also has a say because a united Korea under the South Korean flag would also border Russia. Neither Russia nor China wants US troops near their border in the east.
If all out war was to ever happen again, US led forces shouldn't go all the way to the border this time and just restrict themselves to going as far as securing Pyongyang on the west side and Wonsan on the east side. In that way, Chinese intervention might be avoidable. Less north Koreans would try running away into China and a buffer would be maintained. Give them some humanitarian supplies to help them cope with the shock of losing Pyongyang and Wonsan after a new cease fire has been signed. It would also make the process of reunification less painful for the current South Korean government. Leave the rest of North Korea for a later time.
Well, FWIW at least, just some thoughts...