I’m not sure what would even happen if the GOP voted to condemn their own president. To whom would frustrated GOP voters petition then? Would they fracture into a third party?

The reality nearest to our own where the impeachment attempt succeeded is the one where the Senate was D-majority that year. Only a few seats would have to be different for that, whereas the counterfactual of republicans voting against one of their own would require a shift in the very elements of politics. Imagine a world where a D-majority legislature impeached a Republican president. Instead of pointing to an election, Democrats would have to point to a 1000 page report that nobody wants to read. Republicans would be calling it a "political move" and the whole party would be unified against its fairness.

>I’m not sure what would even happen if the GOP voted to condemn their own president.

The GOP having had enough of GOP President Nixon that they were going to impeach and remove him is what led to him resigning first.

And the country got on just fine.