…because, if he's replaced by Pence, their chances just got dramatically better.

And let's face it. They are pretty revolting.

The GOP just needs to accept that they created this monster, and take steps that it never happens again.

Once again, the GOP "didn't get the math right". The fact that they fielded 17 candidates is ridiculous to begin with, thus spreading the votes out too thin. That loony Tea Bagger 20% of their party mathematically became the driving force in the party. It is simple arithmetic. Party leaders should have been able to figure this out & "encouraged" some of those candidates to drop out. But, instead, they played up to "the Donald" & languished in the publicity he brought them.
Well, here's to free publicity!

dire and more inevitable they will begin to disavow.

If they are up for re-election and they openly disavow Trump, they will lose his hard core voters. In some regions, that might not matter, but in others, it could be YUGE.