I am less concerned about ICBMs and more concerned about Tactical Nuclear Devices falling into the wrong hands. If the government of North Korea falls or weakens they could still fall into the wrong hands. (Same goes for Pakistan etc.)
And even if the government doesn't fall, they've already shown a willingness to help others get nukes:
Where are you getting this from? According to Wikipedia, every member of the UN is a party the GC, and North Korea has additionally ratified protocol I, something the USA refuses to do.
https://en.wikipedia.org/wiki/List_of_parties_to_the_Geneva_...
Pakistan is a different beast. I'm not an expert on the middle east by any means, but it seems to me a lot of nations around it could theoretically start the fight. I believe that would cause a US/Indian/China intervention, if not on behalf of Pakistan (in the case of Chinese and Indian territorial disputes), then in defense of their own interests in the region (the territory).