I sure can't figure out why the world is so scared of what North Korea is going to do. They can't even feed their people or provide simple things like water, sanitation or electricity. The first sign of battle and their huge army will desert.
I rather doubt that. The NK soldiers are three generations into the most comprehensive national brain-washing ever attempted. If they cross the border at all, they'll do it in a human wave attack.
I've no doubt whatsoever that they'd eventually fall apart, but not before they (and their artillery) make a huge mess in a significant portion of South Korea.
The problem:
North Korea has hundreds (thousands?) of artillery pieces pointed at Seoul - a major world-class city, and home to 1/4th of the South Korean population. Levelling Seoul would take about a half hour, and have repercussions across the globe.
NK also has nukes and the means to drop them on Japan. Japan also has nukes and delivery systems. Needless to say, the economic consequences would, er, get the world's attention.
JKI just has to give the word and Seoul and Tokyo disappear (at least in viable theory). The general plan seems to be: wait for the NK system to collapse entirely, which shouldn't take too long. Just wait 'em out.