Of course, coming to terms with China will be an entirely different matter.
1: https://nautilus.org/napsnet/napsnet-special-reports/mind-th...
It would take thousands of cruise missiles to even dent their defenses. You can't use bombers until the anti-aircraft systems are down. It's going to take hours to finish the job, and even then who knows what they've launched in that time. Seoul is an easy target, very hard to miss.
"Not now, I'm busy."
"Put down the phone, Sir. This is isn't a drill."
However the civilians part between Seoul and the DMZ, home to millions, is not going to fare exceedingly well - if the North decides to "waste" their ammo on civilians instead of the military that will be hitting them back.
1) https://www.quora.com/Can-North-Korean-artillery-really-kill...