If I was Facebook, I'd start to think about how to add more value to people's lives. Their monetisation strategy is becoming increasingly annoying and their service is not adding enough value to counter that. People will eventually leave if you irritate them enough (see also comments on https://news.ycombinator.com/item?id=15922022 )
IMHO online social networks have a 5-7 year half life, after that they stagnate and die because the company tries to chase ad dollars (the easiest dollars to get) and step by step degrades their usefulness.
For some reason we don't model business on natural systems (birth -> growth -> reproduction -> death). Seems to me that'd be a good idea if we want to be around in a million years.