Facebook has become more of a phone directory now than a myspace-esque social media site. It won't die unless a better directory comes along. Even if there is a new "MySpace" Facebook will still be around simply because of the way it is organized and set up. People have actual names, actual photos, and various details about their lives (relationship status, work, where they are living). Other sites are basically planets revolving around the Facebook sun. They can come and go, but Facebook will continue on for awhile - at least until Web 3.0 (whatever that will be) is underway.
I got tired of social media years ago. I was addicted to MySpace for awhile, but sites/apps that promote sharing your entire life with the entire world just seem creepy and unnecessary to me at this point. I have a Facebook, but only check it time to time, and never post anything. My gf used to facebook a lot, but I never hear her talk about it anymore.
On a side note, I still remember the first social site I used in College, probably around 2001-2002. It was called hotornot.com, and it was essentially just people posting a profile + pics and getting votes for being hot or not. Maybe people were using it to hook up also, but I went to a party school, so the idea of trying to hook up with chicks online never really crossed my mind to be honest.
It's usage is definitely dwindling, but I don't think it'll ever die because it smartly hooked itself into login data on other sites. At this point I'd say my facebook account mostly exists to log into various accounts, like my ESPN insider account, and the like, and into phone apps. It's also basically replaced my email for genuine email, not shopping/shipping receipts or spam. But the Private messaging is basically my personal email at this point.