Not in the foreseeable future. Essentially FaceBook replaced Phone books and gave everyone a place to get together and meet no matter where you are on earth. The fact that it runs on phones and virtually every electronic device that connects to the internet it is very useful. Infact the biggest threat to FaceBook is competition however Google+ at the moment is a joke as a competitor even once it makes a global launch and anyone can sign up it will never even do a dent to FaceBook.
Now is FaceBook invincible, no. We never saw the day when phone books would be replaced even in the 90's nobody thought that the phone book would be replaced. Nobody saw books and newspapers going down but sure enough they went down. Fact is the internet in its present state guarantees FaceBooks survival.
FaceBook has a unstoppable monopoly on the social network market. Until social networks are replaced FaceBook will always be there. Also unlike print media , the internet isn't going anywhere. Internet may evolve in the future into something far more advanced but it will never die. Meaning FaceBook has the potential to be around for a very long ass time!
-JC7
"In God We Trust - In Games We Play " - Joel Reimer
