Absolute dictatorships are funny things. Romania under Ceaucescu was not far short of North Korea and seemed pretty stable for decades, but then some brave soul said "Boo" during one of the Leader's speeches and it all fell apart within 24 hours: https://en.wikipedia.org/wiki/Romanian_Revolution

I can fairly easily envision the same happening in North Korea, where by all accounts nearly the entire population is dissatisfied with the current state of affairs. One big protest in Pyongyang, and boom.