And what happens when they can't do that?

If they don't have the votes, then they can't pass a bill. But I think that's a low-probability outcome. If they don't pass the bill, then all the Trump tax cuts from 2017 expire at the end of the year - which would set off a bomb in the economy. They can't not do that.

So a lot of electeds in the GOP caucus are going to have to hold their noses and vote for something that they dislike. This contretemps was the Freedom Caucus getting some public assurance that they're not going to be the only ones having to make a vote they hate - they've got the Senate leadership on record that the final bill will have some spending cuts that are going to make frontline moderate GOP Senators unhappy, too.

They can't preserve Medicare/SS/Medicaid, while slashing taxes (both of which the Felon wants).

True, but they can "preserve" Medicare/SS/Medicaid. They'll try to come up with some requirements to fight "waste, fraud, and abuse" which will score as spending reductions by the CBO, but that they can try to spin as not actually cutting anyone's legitimate benefits. If they're worried about blowback from the midterms, Trump can just have CMS refuse to actually implement those measures before the 2026 elections (so no one's benefits actually get cut) - he's perfectly fine with not following the requirements of congressional budget laws anyway.