Hmmmm.... if it continues to morph into a web replacement rather than a social media, it may see a demise. For example, you can now have e-stores on facebook. No, thank you. I'd like to stick to keeping up with friends! Commerce is actually a "turn-off" for me.
I think it'll be here to stay... but, I could be wrong! Who knows -- ten years ago, did we think our phones would do as much as they do today -- so affordably? 20 years ago, only the "upper class" could afford the brickphone... remember?
Technology changes, social patterns change -- good question, CrazyNorw3gian!