Like most such analysis it fails to factor in the importance of network effects that tie people to the social network in the first place.
The main advantage that Facebook has (and all similar social networks across the globe that have gained dominance in those areas) is that they have enabled people to connect in one system a distributed set of nodes of people they have interacted with in real life plus people they interact with virtually.
The value of this network of connections far exceeds any disadvantage that comes from being bored on the service.
Over and again I've seen people claim that they are leaving FB ONLY to come back, the pattern is that those with established and large networks simply can't escape the convenience of being able to chirp to their entire life network (from childhood friends to college class mates to coworkers) via one tool.
This should sound familiar, it is the same reason that most of us have only one major email provider. Once on it, and once we've created our common contact patterns we have no desire to move as telling those contacts our new email is often annoying (it's not hard, but it's annoying).
It's even more difficult on a social network where you have to get each node to MOVE to the new location you are headed to...this is exponentially more difficult the more nodes you have in your network and thus harder for people to move. Also, by consolidating features of interest across the things people do online it makes it difficult to hop.
This is why Google+ is a separate island of people situating themselves there instead of on Facebook, once their networks are built there...they will similarly be immune to hopping over to another network (Facebook being the only viable option in the US).
The correct analogy then for a social network is not any viral or bacterial disease...no it is an oncogenic one, cancer. And as we all know cancer doesn't die .........................until it has either been directly handled via treatment otherwise it goes on to always kill the host. ie. people will die on facebook.
I wrote about this in a blog post from 4+ years ago:
"The proof of all this consolidation is clear in the numbers, users spend incredible amounts of time on the Facebook network...doing all these things they formerly did on different sites. Now, think...with such a huge investment made in having all ones interaction, content and community in one site...what on Earth can get them to switch en mass ?
nothing. Barring a catastrophe on Facebook's end...they will be the last of the social networks and if they avoid Google's response (their only real competition in that they are the only ones with a suite of products that can be woven together to provide a similar experience fast enough and have a user base broad enough to maybe slow their growth) "