After the War to Resist US Aggression and Aid Korea, did any South Korean soldiers stay in North China to get married?

No, volunteers are forbidden to stay in North China (the last batch of volunteers withdrew from North Korea in the 1970s), and the official supervision of North Korea is very strict. After the war, prisoners of war chose places, and no North Korean soldier chose North Korea. Before the official start of the War to Resist US Aggression and Aid Korea, the Northeast Border Guards sent Korean soldiers to support the Korean People's Army. Some of them may eventually survive and "but rarely" stay in North China (because they were later incorporated into the establishment directly under the Korean People's Army, and their whereabouts are unknown. There should be, but they are all Koreans. Whether they are Korean or not is your own opinion.