Personally I don't think that social media will ever fall out of fashion because it's a core human biological need. All Facebook has to do is to keep up with the latest trend, whatever that may be. Maybe people will rather livechat than post static content. Or maybe they rather sit around in a 3d virtual environment. Who knows. But they'll always want to connect with others. Maybe they'll even prefer talking to an AI than to humans but that's still effectively a social interaction that Facebook can provide and connect. They'll simply pivot towards letting you create your own AI friends.
There's a pretty big gap between socializing/communicating as a core human need and this taking shape in the form of current social media. Which didn't exist for 99.999% of our history and is in many ways unnatural.
