Facebook goes first but takes a while. All it takes is for the younger generations of users to perfer a new bleeding edge service and stick with it, then Facebook dwindles. Once another service hits critical mass of users with a critical mass of their personal network on it, that is the nail in the coffin.
Apple is next if they go. I don't think they will fail, they just can't sustain their meteoric expansion. I don't even think that they will slide into some 'uncool Miscrosoft-type status'. Apple's entire pedigree is of design. It's in their DNA. I think they will continue to execute well making high end, high margin, fantastic devices, but their market share will recede eventually, ceding to low end devices that have a good user experience. Apple's "fall" will be more for investors than anybody else. I guess eventually I could see them succumb by a technological paradigm shift that just quickly destroys the market for an entire section of their portfolio. I don't see it terribly soon though, but when computing continues to shrink and become voice based and AI driven, there will eventually be nothing of substance to design potentially, right? What then?
Google is the winner. They are big data. Google Fiber is transforming big data infrastructure. AI, self driving cars, wearable computing with Google Glass. Whatever you think of them, they are a transformative company that is going to own the long game.