The current Democratic party is a mix of liberals and progressives working together through compromise, that would not change. Conservatism is the minority and will continue to dwindle as boomers die out.
A third party is inevitable in the landscape of politics of this country. The upcoming generations will be overwhelmingly liberal/progressive, making conservatism that much more of a minority where moderates will no longer be able to straddle the fence for survival. At some point the liberals and progressives won't see the need in working together on compromise since obtaining a majority vote of the 2-halves for Congress and the WH would not be far fetched and would give them a majority.
The foundation of division is already set, it only gets worse from here, especially when Dems regain power.
To be honest I think your prediction of conservatism becoming a minority position is wildly optimistic. Some people are going to get more conservative as they get older. It's hard for me to imagine that splitting the left-leaning vote will help anybody other than the GOP.

Certainly only helped them in 2000 and 2016.