On a more practical note, I despise Facebook, but I don't think it is going to fade into oblivion. It may become less relevant, but it will never fully disappear, especially as it snaps up these new social networking channels like WhatsApp and Oculus.
I think Facebook, if anyone, knows best how to defer these types of scares. They have some of to brightest minds constantly worrying about these problems. Remember when Google+ came out and people thought Facebook was doomed? Well they survived - and that was a Google effort mind you. At the end of the day Facebook delivers a good product, not to mention established themselves as a legacy platform. I think Zuckerberg stated once that he wanted to be the "dial tone" of the internet. I think they have accomplished this. And as technology continues to develop, Facebook will try its best to stay up to date.