I think it is far more sensible to start by assuming that North Korea is deterrable. That way, one does not act in ways that trigger an unnecessary war, nuclear or otherwise (either of which would be devastating to South Korea, Japan and the international economy). If North Korean leaders just care about staying in power, then:
- don't threaten to change their regime since that might cause them to attack.
- don't try to take away their ability to retaliate since that might cause them to attack.
- don't make them think an attack is imminent since that might cause them to attack.
- do make it clear that their regime will face much stress if they do attack--via retaliatory strikes by the US.
Any hubris about taking out NK's capabilities to do massive harm to the neighborhood needs to confront the realities that:
- Past SCUD hunts by the US have gone poorly, so the idea that the US could nail all (and it would have to be all) of NK's missiles is wildly unrealistic
- Even if NK's missiles are blown up on the pads, NK has way too many artillery pieces aimed at Seoul (as well as various conventional missiles aimed at Japan) so that the opening hours of a war would kill many, many thousands if not tens or hundreds of thousands. Any effort to send the South Koreans to shelters before a war would signal to NK that a war was imminent and they would start firing, so not so much surprise.
- Probably at least one North American city would be hit by a nuclear weapon. Missile defenses are wildly overrated so our best hope would be shoddy NK missiles.
Oh, and to make matters more fun, the North Koreans have to worry if Trump is sane and deterrable. I am not so sure.