Goodness gracious, the potential End of the WorldTM if the Kim regime falls is not the problem, the fact that the Kim regime hasn't fallen is the problem.
No, it really isn't.
The Kim regime falling would be a disaster that would make surrounding nations and the world wish fondly for a nice little nuclear exchange instead.
Millions upon millions of refugees, streaming across the Chinese border, the DMZ, and over the sea on anything that might float. A heavily armed military suddenly desperate and without leadership. Nuclear, chemical, and probably bio-weapons going missing in the chaos. It would be a massive disaster, that would make everything the US has done in the Mid-East since the Gulf War look like a walk in the park by comparison.
