The ROK would have its hands full running the north or former DPRK not to mention coming to a gentlemen's agreement with the PRC on a border zone at the Yalu and with the US on either withdrawing its troops at long last or keeping some on the Korean peninsula in order to "show the flag" ("If any of you get out of line, you know we are still here") and also keep any local Koreans employed with the US forces ( Jobs, ya know).