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.
You're forgetting the inevitable campaign of cyber-sabotage, a handful of conventional terrorist attacks and assassination attempts on whatever or whoever the North Koreans consider good targets, plus terror and conventional strikes with chemicals and bioweapons, and bunch of nuclear bombs smuggled to their targets. (They probably have more bombs than they have ballistic missiles for.) Maybe a couple dirty bombs somewhere if they've got surplus nuclear material. Plus the
accidental releases of all the above as we and whoever else is joining in bomb the North Koreans back to the stone age, again.
Much better than talking to them. Who knows what that could lead to.