We've had that exact scenario happen before, where one party died off entirely. Within a couple of years, they split off again into two different parties. And that's exactly what will happen again. Democrats aren't some kind of monolith, they have everything from Corporate Dems like Pelosi that made millions with her inside trading, don't-rock-the-boat neoliberals that would be considered conservatives anywhere else, to leftists that would love to eat the rich and get money out of politics using just about any means necessary.

They're only grouped up now because the alternative is well... Republicans.