Looking at the demographic shifts, this election has all the hallmarks of a Nixon 1968-style result that brings about a major, long-lasting shift in the status quo. That being said, it also feels very similar in a lot of ways to John Kerry's loss in 2004, in that it could be an opportunity for the Democrats to get their act together over the next four years and come back when the incumbent hits the term limit.
Basically, either the Democrats can re-establish their connection with voters, find themselves another Obama (hopefully not literally, but Michelle probably would be one of their better options right about now), and turn this into a necessary fail that provides them with a platform for greater success in four years. Or they can double down on what caused them to lose, run another George McGovern next time, and spend the next twenty years in the electoral wilderness.