I don't think it's about the presidency. That's a wash, and every Republican leader with a brain knows it.
I think what we're witnessing now is a party trying to sort out how to best mitigate the damage.
I think Republicans are ultimately going to conclude that letting Trump go to November will be a lot more toxic for the party in the long run than biting the bullet and expelling not only him, but also his supporters that will continue to keep Republicans from producing winners from their primaries from here on out. The Republican base is just too out-of-step with the rest of the country. Burn them all.
Long-term, they're better off leaving Trump in. After the 2012 election, there was an internal critical analysis of what the GOP had to do to win future elections, which was essentially summed up as "Be more liberal/less racist". What they've done is the opposite - they have literally ignored everything from the analysis - and when in the Primary they could've followed the new playbook with minorities and women, they instead chose to not criticise Trump too much, in order to court the racist/misogynist vote.
Leave Trump in, and he'll do what the analysis couldn't do - handled correctly, his loss will affect a major change of the Republican party, since it'll show that it can't be the party of racist men who want to tell women what to do if they want to win an election. Dump him and the opinion will fester that "If only we could show everyone how right we are with our views, we would win".
Edit: That analysis: Growth & Opportunity Project (pdf)