When I went there over 20 years ago, one of the first orders of business was to get a briefing on the situation....and the situation was that both sides had thousands of rockets, and the border would instantly become a 30 mile wide band of complete destruction. And I distictly remember a strong emphasis on being ready for the norks to use nerve gas.
My unit was at a briefing on Christmas Eve by a 3 star general. He told us to expect 75% casualties within the first 24 hours.
And Seoul is what,
32 miles south of said border!