My guess is that her plan is to either become the Republican nominee of Trump goes to jail, or (more likely) set herself up for a 2028 campaign. Endorsing Biden would end her prospects for the latter, so it's not going to happen.
The GOP is the party of Trump now. Haley came out swinging at Trump in the primaries. Her career as a GOP politician is over. They’ll run Don Jr. in 2028 before they run Haley.
Doubt it. Trump is hanging on by a fingernail. The entire GOP infrastructure is teetering on the edge with it.
They get slammed every election recently, Roe v Wade is against them and their strongest part is nobody wants Joe Biden. GOP is on life support brother.
The GOP is the party of Trump insomuch as it gets them votes from the unwashed masses. If Trump goes to jail and public opinion somehow starts to sour, they'd endorse someone else like Haley instead.
More likely, though, is that MAGA voters continue to support any politician who turns Trump's persecution complex into their campaign goals. Maybe they win the presidency and the fascism train kicks on under some Trump sycophant, or maybe the continued extremism and fragmentation of the Republican party costs them more and more elections until the movement eventually just fizzles out.
Any time you see the question "Will [republican] do the right thing and..." the answer is almost always no. No, the republicans will not do the right thing, and we have decades of evidence of that. You may get the occasional right thing (like McCain and the healthcare vote, or Cheney and the J6 committee), but by and large my money is on them doing the wrong thing.
Remember that episode of South Park where the KKK endorses one side and no one on that side likes it? It's like that. If she endorses Biden, that's a sign a troubled times.