A military response would be a disaster given the size of the armies in the region and the proximity of Seoul to the border, which puts it within striking range of North Korean missiles.
The big question is: why would North Korea disarm now? It has stalled on its multilateral agreements in which it promised to disable its plutonium production facilities at Yongbyon. Its nuclear weapons guarantee the survival of the regime. Negotiating away its nuclear arsenal would be to cast away its only bargaining chip. It has just confirmed to a U.S. scientist that it has a uranium enrichment program and 2,000 shiny new centrifuges — which could provide a second path towards the bomb. The revelation demonstrated that the international sanctions against the North have not worked.
For all these reasons, I can’t see a happy end in terms of the logic of U.S. and South Korean policy. The only certainty is that the Pyongyang regime will collapse, whether it be a “soft landing” or an implosion. It may have unpredictable consequences, but it will be a cause to rejoice.