It really is all bluster. Both Choe Sang-hoon of the New York Times and Ask A Korean have reached the same conclusion: so long as the Kaesong Industrial Plant stays open, war would appear to be unlikely.
Of course, the North Koreans read the news too, and since they’ve run out of nasty things to say about America and the South, and since they’ve tested just about every weapon they possess, they may close the plant down just to screw with everyone. Remember, in spite of the kamikaze rhetoric, the North is just as uninterested in war as everyone else: these relentless provocations are meant to secure the reputation of their new leader as well as the money and food their country requires. The North Korean economic model goes like this: build weapons, threaten the planet, get money. The world’s economic model goes like this: build things, sell them, get money. That’s the difference, and that’s what these people are after.