Even if Norks levelled Seoul, and planted flags, they still wouldn't win.
All the things that made Worst Korea successful, are economically and culturally abhorrent to the norks.
After Norks supposedly kicked arse, they'd gather around the rubble and say "now what"?.
Then the Northern end of South Korea would become just as dysfunctional and worthless as the rest the rest of "Best Korea".
Then of course, the Sorks, Yanks, and maybe even Chinks/Japs press the reset button on Best Korea, starting a 4 front war that lasts maybe 6 days at most. A race to take as much land before the Chinks occurs, much like the race for Berlin previously.
The Chinks and everyone else grumbles over their new prize, whilst wondering what to do with a few million impoverished, worthless Norks.
Of course, not bound by humanitarian limitations, the Chinese find a more profitable solution.>Cute Nork mail order brides when?