One should not underestimate the Zuck.

It's hard to have a conversation about Facebook's future without taking into account that it also owns Instagram and Messenger, which are immensely popular social networks... and Instagram in particular has been super aggressive in going after and growing its userbase. Its recent battle with Snapchat should be an indication of the lengths Facebook will go to in order to retain its userbase.

In terms of Facebook itself, worth noting that the platform is still seeing DAU growth:

That said, I'm not sure of the geo/age breakdown of that growth, which is probably important.

In terms of whether it will go the way of Myspace... I don't think so. Myspace was sold to a gigantic company who didn't have the knowledge or speed to adapt its platform for the evolving needs of its users. Facebook knows EVERYTHING about its users, and has the ability to rapidly push out changes.

Also keep in mind that Facebook is not afraid to reinvent itself, to force massive change on its users overnight. Don't underestimate the Zuck :)