I think it's been mentioned before that standardization of social networking protocols might work, to the point that they become part of the Internet itself, like e-mail. I think it is only a matter of time (2-3 years) before the majority of Internet users will simply use distributed systems where their social data will be spread over several services (proprietary or open source), and the sharing of that data will follow a standard protocol (maybe a future blend of ActivityStea.ms, Salmon, and others).
Facebook will survive, most likely, but I think its influence will slowly wane to the point where they will be just another "media company" like AOL and Yahoo.