While the Democratic Party will need to reorder itself should it wish to survive, I think the only result would be pushing the liberal wing out to join the Greens (or whoever). The Democratic party swinging toward moderate might attract away liberal Republicans, leaving the GOP as a more fundamentally conservative party. When the vote is 51-49 (or somewhere thereabouts) I can't imagine either party letting any block walk. There cancer is within them and the cure will cost them several years to recover. Add to that that they are already the party of "right now at this moment" and it will be difficult for them gain a consensus on what can be done that will be effective.