Facebook and Google will stagnate and grow into their valuations. Google particularly is trading far beyond where it should versus its now modest growth rate. ~37 times earnings, $700 billion market cap, for 10%-15% annual growth over the next five years? No thanks. In the not very distant future, Google will pull a Microsoft and begin paying out a dividend, after this latest stock market bubble ends and their stock returns drift to mediocrity.
People said that three, five, ten years ago. What is happening is that the market for mobile and desktop ads and e-commerce is growing, combined with increased market share for these three companies, creating a double tailwind. I'm certain Google, Amazon and Facebook will not suffer the fates of Exxon, GE, PetroChina, Royal Dutch Shell, Citigroup, AT&T, Gazprom, BP, Toyota, Bank of America, China Mobile, HSBC, ICBC, and Walmart. Part of the reason Amazon, Google, and Facebook will be permanently successful and are so resilient is because they have market dominance, impassable moats, ubiquity, and are mostly immune to global macro conditions, whereas commodity and banking companies are much more vulnerable to macro conditions. It's much easier to create a steel, drilling, or mining company (look at all the overnight fracking companies that went bust in 2015-2016) than it is to, say, get 1/6 of the world population on your social network (Facebook), every website and phone displaying your ads (Google), or every consumer buying from your store (Amazon) (and also the cloud hosting services). http://greyenlightenment.com/will-the-silicon-valley-tech-fo...
But also, some of those companies you listed pay huge dividends, so when you factor those into the returns, it's not stagnant.