So, overall, the idea that Right-Wing populism will dominate the GOP is ludicrous, as this would basically forfeit the entire country to Dem control. If such a scenario were to occur, its likely it would be a repeat of early American politics, with the Dems being the Democratic-Republicans, and the GOP being the Federalists. One party would have basic control of the entire government, and the other would be a more regional party. And, if such a scenario were to occur, it would likely cause the D party to split in two, and for those to be the new two parties in our system.
The thing is, it doesn't matter what kind of losses such a change in the party triggers. It makes sense why one would think about it like this, but you're being too rational and focused on electoral performance. This isn't about winning or losing so much as it is about what people believe and what the GOP pols believe they need to deliver for their constituents. You could argue that the changes in the Democratic Party through the late 70s/80s-onwards triggered its massive losses of power post-1994
(I'd disagree in a number of ways, but I digress), but even with people making this connection, it still took decades for significant opposition to develop to the Third Way stuff. That is what will probably happen in the GOP. The Republican Party is really having quite an unflattering moment for itself. The policy agenda of the country club Republicans is out of step with an increasingly working class-heavy base, and it can't stay like this forever. However I'm sure after Republicans get cast into the political wilderness for a good long while, they'll have their own internal backlash and the party will shift again.
