I've heard about a few possible scenarios:
1. Haley is going to get a job within the administration in the new year, to show that the Republicans aren't anti-woman or anti-minority (she's the daughter of Indian immigrants). Quite possibly for 2020 they'll kick Pence to the curb and run a Trump-Haley ticket.
2. She's setting up for a run of her own, probably challenging Trump in the 2020 primaries. She probably can't win, though--the Republicans have too many winner-take-all contests.
3. She's setting up for an independent run, trying to bleed just enough of the Republican vote (particularly in the South) to keep Trump out. Kasich might do the same thing with the Rust Belt.
Oh I'm sure she'll run for President in 2024. No one is going to challenge Trump in 2020. He may be one of the most hated presidents in recent times but he is the most loved president by the Republican party.
Anyone who challenges him that's an elected official is calling for their throats to be cut.
Ironbite-probably see a few other "billionaires" try to unseat him.
Anyone trying to challenge Trump from within the Republican Party will not succeed.
What might happen is that Haley and/or Kasich make runs as independent candidates, focusing on their particular regions where they can draw off votes (from anti-Trump Republicans who can't bring themselves to vote for the Democratic candidate but can sleep at night voting third-party for a Republican they would be fine having as President--never mind that there are basically no policy differences between them), and effectively ensure that the Democratic candidate wins states like Pennsylvania, Michigan and Wisconsin, and probably also Ohio, North Carolina, and Florida--who knows, maybe even Texas.
Both would, at that point, have been out of any elected positions for a good time at that point.