We don't really have a term for people who have lived abroad and have returned. However, we do have a word for Koreans living abroad, 교포 kyopo. Kyopo is a pretty broad term that ranges from Koreans who have immigrated to different places and have settled down to descendents of Korean immigrants as well. It basically means Korean diaspora. I guess not many of them have returned enough for us to have a word for that group of people, unless, as pointed out above, they are students. When 교포 Kyopos return to Korea (for visits), we just still refer to them as 교포, or if they settle back down in Korea, I guess we don't really call them kyopo anymore since they are living in Korea, but more say that they were kyopo, or would just say that they used to live somewhere else.