Primaries serve the same function as the Republican Liberty Caucus, ie, to let libertarians think they have some influence as they’re being ignored.
If they end up going with someone other than the top or close to top finisher they are toast. I think people will vote democrat to spite the party and throw all the republican’s out of office.
Fact is two anti-GOPe candidates are at the top of the field. If they rig it to keep it a GOPe person it will backfire worse than just going with Trump as the nominee.