Facebook has over 500 million active users.207 million of these are in the U.S. ! in every 13 people across the whole world has a facebook account and close to half of all these people are logged in at any given time. 48% of 18-35 year olds have a facebook account.
In my opinion i would think the facebook will only grow and grow because the introduction of facebook on smartphones has gotten massive and with so many people owning a smartphone and with facebook making their site smartphone friendly i would say that in time facebook will grow and will become a very good marketing and advertising tool if used correctly. 28% of all facebook users are using it through their smartphones.
Facebook had a record breaking 750 million photos uploaded during the new years week end. This is by far more than any other site in the world.
So based an these figures alone i woulsd think that facebook has a few years left before it becomes RIP and with their numbers growing yearly I would find it hard to believe if it were to cease to exist any time soon.!!