I think that we Democrats can start winning again, but it will take some change.
I encourage people, especially conservatives, to stay in the party (or join it) and do exactly that. I don't envision a future Democratic party that would be a clone of the Republican party. Because the Republican party already exists.
What I do envision is a Democratic party that truly embraces minorities within the party (e.g. pro-life, anti-tax, religiously devout, etc.) and acts as a loyal but vigorous opposition to the Republicans. I think a sort of libertarian/moderate left/religiously tolerant/ constitutionalist party is well within the realm of possibility. I also think it could be a winner.
Unfortunately, I also think that a far more radical/ socialist Democratic party is within the the realm of possibility as well.
Let me leave you with this to think about. The future of the Republican party is tied to that of the Democratic. Many of the problems that the Republican party has (e.g. RINOs) stem from some of the ongoing problems that the Democratic party is contending with.
food for thought.