North Korea is more rational than most people tend to believe, but not rational to the level that, say, Iran is (and they're far more rational than people tend to believe). They do believe the world is out to get them, but they also know enough not to pull the trigger themselves unless there's no other choice--though that may include taking the nation down with them if someone tries a coup.
Absent an enlightened successor to Kim Jong-Un in about 30 years, any shift in that impoverished country is likely to be bloody, violent, and involve a lot of carnage outside its borders.
Where I'm not inclined to disagree much... It's obvious that an overthrow of the Kim dynasty will be bloody, I'm inclined to believe that if it happens it will be quick and the violence will be fairly localized and unlikely to flow over the border that much. What WILL be an issue is if the conflict lasts very long and the population starts flooding over the borders as refugees, mostly into China.
The question that should be going through everybody's minds though should be what will trigger such events... Lit'l Kim spends lots of time thinking about this and is actively trying to keep it from happening. When any of the powerful in the government and military have even a hint of disloyalty, it's off to the concentration camps for your family and death to you. Think of it as a bureaucratic cottage industry in NK. The quickest way to advance is to give states evidence on your superiors for what ever reason you can. Kim uses this to stay in control, but eventually the truth will get out, that the rest of the world isn't starving and tiny NK isn't the huge military power, shining country on a hill that everybody want's to be a part of. That the Kim's are just self serving egomaniacs who have ruled with iron fists, forcing the people to suffer while living in luxury unimaginable to the common folk.
All this ICBM and nuclear weapons garbage is just a rouse to keep the Kim in power anyway. He has to keep showing progress, keep showing is people that he is still potent "Large and In Charge" supreme commander of the military the world fears most. This whole thing is designed to appeal INTERNALLY to the people of NK, who generally believe what they are told. Kim is being forced to produce better and higher demonstrations of NK's military power, to keep the dream alive that NK is the world's lone superpower, able to beat the USA back and keep it at bay. Once that image cracks, Lit's Un will be reduced to a skid mark on the runway of history.