Kind of. But it shouldn't be a mental model where something like Facebook, but better, comes along. Rather, you should expect something that fulfills the same emotional, practical need or occupies time that makes people use Facebook less, but fulfills a need that better clicks with what people want.
As an analogy, consider how Apple and Microsoft flipped places. It's not that Mac OS was like Windows but better and supplanted them. Rather, smartphones changed the game in such a way that Microsoft's core strengths didn't seem so strong anymore. Apple was able to innovate in such a way because of their DNA as a design focused product company, but those strengths didn't get to shine until the paradigm shifted to favor cohesive product experiences rather than versatile software platforms.
So the thing that supplants Facebook won't look like Facebook, it'll be some better way to keep in touch with people from previous walks of life, get in arguments with your distant family members, and share photos. And it won't happen all at once either. It'll probably sit as some obscure niche for a while as it slowly refines itself and evolves.
That was a dependency game.
Windows had created an incredibly strong lock-in effect, leading it to become like an invincible bastion. But at the same time, the bastion's walls make it difficult to connect any device from the outside to it. The same stones the walls were build with are what is dragging the Microsoft ship down.
What we need to realize is that FB is creating and exploiting dependencies, too. I could imagine that a new wave of communication tools would be just much more economical with our time and attention, and would match both to the real importance the people we communicate with have for us.
Yet similar services like AOL, Friendster, and Myspace were once big and are no longer what they were. I have no idea what will possibly supersede Facebook but I bet it will be something out of left field.
I think we are entering much more violent times, where huge corporations will see a crashing end.
If there will be great, easy to use, easy for user alternative to Facebook, that will be able to fill all the blanks quickly, would Facebook's value, stock and revenue withstand for example 250 Million user drop? Those would be the users that are unlikely to come back, and this would initiate huge migration.
There is a time when a company screws one time too many, disruptor shows up at the right time with the right cards in its hand and literally syphon the value out of the big company. This happened many times before. See how Google showed up with better solution, very adaptive strategy and no annoying noise and rip apart the whole search engine niche.
This is a very dangerous game, with a lot to lose. It was the same with any other, now dead, giant on the web. Only because people are still using Facebook now, does not mean, that as soon as a worthy competitor will appear, people will move et masse. Facebook is a necessity now, but it might be not, for example, tomorrow.