But not if the funds are back in South Korea.
Not true. The US has an extradition treaty with South Korea. That includes ill gotten funds as well as people.
The US seized something like $16B from El Chapo - and he’s a Mexican Citizen. Since the US seized funds from all over the world in that case (including Mexico, Cayman Islands, Switzerland, etc.) I read yesterday that Mexico will ask the US to split those asset forfeitures with them.