Massive artillery barrage on Seoul, funneled troops including SOF push south, potential nuclear ICBM launches on Seoul, Tokyo, Pusan, US west coast. We know where they have some toys but not all of the chest, let me put it that way. 30 to 40,000 KIA within the first two hours. Guaranteed NK retaliation via the methods above and maybe chem/bio launches, insurgency. Bad stuff Higgins but the US and SK would win it in the end.
I think we should lance the boil before the infection gets any worse. The U.S. shouldn't be afraid to do whatever it takes. Conventional bombs. Have some agents infiltrate NK military establishments and knock out key personnel with chemical weapons. Prior to doing all this, rapidly withdraw all US and SK personnel from border/DMZ zone. The first strike should be at all nuclear sites in NK at once, to ensure they can't launch anything at Seoul.
Also, work with China to ensure they have NK's northern borders lined with mines (this planting of such can occur months ahead of the actual assault)