There is only one way to end this and unfortunately it is with a nuke. The biggest threat to the south is Nork artillery. Take that away and the north is done. That’s been their strategy for 60 years and it hasn’t changed.
Hit the Norks with multiple nukes, both strategic and tactical - Put two strategic 15 MT nukes on Pyongyang, and hit all their military installations with tactical nukes. Destroy their command and communications structure in a 1 millisecond blinding purple flash. There will be no artillery remaining to hit Seoul.