A company, platform, or technology can "die" in the sense that it loses the initiative, and more importantly, the ability to drive an industry and/or conversation, even though it hasn't yet died.
Apple was "dead" through most of the 1990s. It simply didn't matter, outside of the graphics and design areas, and for a very small cadre of fervent fans. The turnaround shocked me.
IBM very nearly died in the early 1990s, as its place as the center of the business computing world was shaken by anti-trust actions, Microsoft, and the upsurge in Unix vendors. The company's never fully regained its former footing, though it did recover largely.
Microsoft has been in the process of dying for most of the past decade. A highly symbolic moment for me was when The Economist newspaper ran a cover showing the leaders in tech: Apple, Google, Facebook, and Amazon. Microsoft wasn't even mentioned (it reminds me of an earlier revealing moment when the CEO of Visa International named the company's biggest rivals: MasterCard, AmEx, and Microsoft -- I guess it didn't pay to Discover...).
Sun Microsystems was fingered for the walking dead as Linux became ascendant, with its acquisition by Oracle (a panic response of both companies, coming at least five years too late to do either any good) coming long after it was obvious the company had not only staggered but was mortally wounded.
One thing to realize is that a fading icon is often not replaced by a direct competitor, but by one which addresses short
Facebook has dominated Silicon Valley for the past 5 years, stealing initiative from Google (who seems to be somewhat winning it back). Part of the situation is that "traditional" social networking is becoming passe, in part because it's become too Byzantine, and too intrusive. Social networks -- real social networks, not the online instantiations of them -- work best when the groups are relatively small, Dunbar's number is respected, and there's a level of insularity around any given group. TheFacebook at Harvard had those features. Facebook, Inc., 1 billion served, doesn't, and cannot. Another secret is that one of the secret sauces of social is photo sharing (still hard if you don't have your own dedicated server), and that services are sprouting up to offer this (Imgur, Snapchat, etc.), which is essentially disrupting the former Social glue much the way Craigslist gutted classified newspaper advertising in the late 1990s.
I'd like to think that the constant drumbeat of surveillance state revelations we can thank heros and patriots Edward Snowden, Laura Poitras, and Glen Greenwald for are having an effect, though I think that may be giving the general public a bit too much credit. Not totally sure of that though.