If the DMZ broke open and the Koreas were reunified, I'm convinced that most of the women would go into the adult entertainment industry or those dim little cottage industry factories in Dongdaemun. They'd also make good countryside wives, and marriage immigration would come to a screeching halt.

The men would be put onto fishing boats and South Korea would rid itself of 3D workers as a huge pool of unskilled labor suddenly opened up. They actually paid some of the workers at the Kaesong complex with chocopies (like a southern US moonpie) and I'm sure companies here would try to pull something similar with wages.

The North Korean introduction to modern life would be being eaten alive by the demands of the market economy. Some North Korean defectors want to go back. They see bootlegged South Korean soap operas where everyone's rich and beautiful and they think everyone lives in a Pyeongchang Dong mansion worth twenty million won a month in rent, so they defect, wanting them some of that, and end up in a dirty old villa in Myeonmok dong sitting on the floor eating shin raman and drinking dong dong ju.