That said, Facebook does look a bit wobbly right now. I could see it start to fall within 3 years from today, but not vanish completely in that time frame. Once it starts its decline, it will likely never recover and eventually will disappear completely. It's a social network, so everything is driven by social trends. If Europe or the US decides to grow some balls and stop Facebook from buying up every start up with a chance to compete with it, and a new network or networks disrupt it, then once the ball starts rolling and people jump ship for the new networks, their friends will follow, and then their friends, and their friends, and so on. That's how Myspace died.
Microsoft is different. When this prediction was made, it did look very wobbly too. But the new CEO has diversified and future proofed the company a bit, so it'll stay relevant a bit longer. It would never disappear though, just become irrelevant, like IBM. IBM invented the ATM, the PC, the magnetic strip on the back of credit cards, the barcodes on our products, the floppy disk, the hard drive, and yet after all that most people who know who they are understand that they're basically irrelevant now, even if they're still huge. I could see Microsoft meeting a similar fate someday, even if Windows and Office keep it alive for a long time after it's relevant.