Everything peaks. No matter how long you think something is going to last, something new will come along and replace it. Twitter eventually will, so will Tumblr, and every social media network will eventually follow the path of Myspace. Facebook might not be going extinct any time soon, it certainly seems like it will be going down that path, as people are getting tired of the constant hacking, spam, and "share this if you believe in god, ignore if you worship the devil" "like this if you support this little girl with cancer, ignore if you want her to die" types of things.
When MySpace was out, no one thought it would ever just "disappear". Then, the next greatest thing came out: Facebook! Soon enough, everyone made the switch from MySpace to Facebook. I'm sure this will happen again. A new company will come out with a brand new social networking website, offering more features and better options then Facebook. People will switch over, and Facebook will become a thing of the past.
There were others before MySpace, does anyone remember Friendster? Let's ignore the past for a minute, Facebook isn't exactly a glimmering tower of excellence. For the better part of two years they have been compromising peoples privacy and selling their members to public entities. Not certain what the Facebook killer will be, however it is an inevitability. technology and people move on.
I think that it will, Facebook has led to a lot of problems with our world. The instant communication is not always good. I do not want people to know when I am just headed out to the store or just getting home from a hard workout. People share way to much on there.
Facebook is huge and it will take a while for it to go away. But MySpace seemed that way at one point, and every big site I can think of has peaked and then slowly declined. Already, people are starting to think of privacy violations the moment someone mentions Facebook. It's reached the point of being popular enough for people to find it cliché. So once something comes along that could replace it, which always happens, Facebook will fade like everything else.