Obviously, quite an uneasy situation with this fanatic country, and no military solution seems to be possible. The choice would be between bad and very bad scenarios.
IMHO, they will never be a deadly threat for US (even if they succeed with ICBM) because deploying enough Aegis systems is quite possible considering relatively small geographical area of NK. But what to do with SK and US bases and troops there since they may be within the radius of artillery/MLRS ? Even now they can reach Seoul...I have doubts that so many Patriots and THAADs would be possible to deploy to counter their massive use. Their ships and subs count, too. Though they will likely be eliminated after the first shot, who knows what might be targets of this shot?
IMHO, the only solution might be transformation of the society by their Southern brothers, so that German reunification scenario would be possible sometime in the future. But SK did not succeed much on that front, so far...