Microsoft ? Hell, no.... it won´t, they have a lot of business going on.
As for facebook, I don´t doubt it will die soon, I just can say how long it will still survive. 3 or 5 years. Maybe less, maybe more, as most internet trends we have seen in the past 20 years. Does anyone remember all the fuzz around Second Life some years ago ? Vanished. And what about the craziness that was myspace ? Ghost town. And chat rooms, ICQ, Yahoo groups ? Done and gone.
Only forums and blogs still persist but in a very different way that they used to be.