Post Facebook apolcalyse

OK so whats comes after Facebook. Before Facebook we had Friendster, MySpace, Friends Re-united, Bebo. Can Facebook make a critical mass such that the users cost of leaving is so high they maintain their user base for a long time and don’t succumb to the problems of its predecessors and explode into space and the annals of history? Or will this be a flyer for a while until some of those recently minted Facebook employees take on their Alma Mater.