You're right.
The flip side of this scenario is:
If the next President is a Conservative (and this can only happen WITH Tea Party support), the next national election will be a Tea Party victory AND the end of the GOP, as well!!
The coming Presidential election is a lose/lose for the GOP. THAT train has already left the station WITHOUT the GOP. That's how I see it.
The Republican Party had a vigorous "youth," a very prosperous "Middle Age" from the 1870's through the 1920's, a satisfying old age until the the 1960's and is now a collection of crooks like Boehner and McConnell who have sold out to the Democrats in return for safe seats and favors for wealthy contributors.
The Republican Party will not have a dignified, evolutionary passing. It will be a horrible death on life support from the Democrats, who seek to keep weak opposition alive merely for the sake of the appearance of "democracy." The death of the Republican Party will be all the more horrible because it us who must pull the plug on this collection of self-serving poltroons.
Unfortunately, the Republic is at risk. Ain't nobody wrote she'll last forever.