It'll be a mixture. Outside of Hillary, I don't see there being a democrat candidate who can galvanize multiple demographics (blacks, Hispanics, youth vote, white liberals) as effectively as Obama has; he's a political phenomenon in that regard. But I do believe the actual democrat engine of early voting, caucusing, and organizing can be passed on to another candidate as long as he or she is an exciting candidate; so the organization will be there, the question will become who is best able to exploit it. For instance I couldn't imagine John Kerry coming close to what Obama is doing on the grass roots.
It's also worth noting that Howard Dean basically built the framework for this in 2005 and 2006 with the DNC 50 state strategy. The party just needs candidates who realize the importance of the grass roots. Obama made a lot of friends with the DailyKos, MoveOn, unions, etc types. That's why I don't believe Andrew Cuomo can be an effective democrat candidate: he turns off all of those groups.
