Nikki Haley and POTUS just announced she would stay on as UN ambassador till the end of the year. My guess is that her next move will be one of the following:
1) Lindsey Graham steps down as US Senator from South Carolina and the governor appoints Haley as Graham's successor.
2) With the big developments in North Korea, Haley gets appointed as US Ambassador to North Korea, or perhaps to a unified Korea.
3) After a period of quiet, Haley gets appointed to a Cabinet position (as UN Ambassador, she is just below Cabinet level.