Everyone keeps talking about this magical missile. It doesn't exist. If they use nukes, they will be short range tactical strikes, not long range strategic ones. The long range claims are only that. They just don't (yet) have a missile that can carry a payload over that distance, nor do they likely have a payload that could be delivered via missile light enough to be practical.
But even so, they don't really need them. Military experts say that if nk were to launch a conventional attack against sk, they would quickly overwhelm both us and sk defenses. They have a huge numerical advantage and they are a professional army. Sure, we have better tech, but the analysis shows the numerical advantage would overcome our defenses.
Their losses would be astronomical, but they could win if they had the discipline. Keep poking and provoking, and sooner or later they are going to explode.
But the missile thing is just fear mongering. Both sides are guilty, but nobody really takes it seriously yet.