I don't think Facebook will go away any time soon but it will become another Yahoo and that can only be a good thing for the ecosystem in terms of opportunities.
No one uses G+. I'm relatively technical, and have 40-odd friends there, and the last post was from December 2012 (and the one before that? July!).
The problem with Google and social networking is that social networks initially catch on by being 'cool'. Myspace, Facebook, Twitter, Instagram, Tumblr, Pintrest - they were all initially cool, and got that market right. G+ has never been cool (nor, in my opinion, is Path). If an app is used by a small group of people because it's cool, then it will grow. If it's used by a group of techies because it's better, it will grow until (at most), it covers the entire subset of techies. G+ isn't going anywhere, at least until there's a major rebrand.
When FB introduced the newsfeed, people thought it was supremely creepy and they complained. Now they probably don't remember what it was like without it. When the timeline was introduced, it was the same thing. People complained about business accounts, apps, searching, photo tagging...every major change gets loads of complaints. And yet most people accept or even love those things within a couple months, and FB has continued to grow monumentally.
I see no reason to imagine this visual redesign or even the upcoming graph search will be any different.