I would say it's absolutely clear that the North Koreans are motivated by regime survival and that their behaviour is consistent with that aim.
With regard to the issue of behaving in line with traditional deterrence policy, I think it's important to remember that the deterrence policy we are familiar with from the Cold War era was developed over a long period of time and had a fair number of very tense moments. The risks of miscalculation on both sides are high in those kinds of situations, and the friction, particularly within the region between North Korea and its neighbours, is such that, as we've seen in the not-too-distant past, local conventional conflicts can spark up very easily. If there was a perception that the regime's survival was threatened in one of those situations, that could have very serious consequences.
I would be cautious about throwing around the phrase “deterrence policy” in the historic sense we have vis-à-vis the Americans and the Russians.