This is 1974 and 1995 all over again. Back in those days both AT&T and Microsoft pretty much wrote their own rules for reconciliation with the federal government.
I'm seeing this whole affair with Facebook in pretty much the same light as that.
Facebook may spin off a couple of ruined (ruined by Facebook) subsidiaries, call it a day, and continue to do what it's always done, just like with Microsoft and AT&T (Facebook will absolutely retain it's core structure and business model).
These big companies are very rarely ever hurt by government intervention into their trade practices ... At&T for example lost nearly 70% of it's book value in the beginning, but rallied back in a sense when it was purchased by SBC in 2005 for 16 billion dollars. AT&T might have been broken into Baby Bells, but it still owned all of the hard lines across the United States and all of those Baby Bells had to pay AT&T for the use of those lines.
Same deal with Microsoft. The company was never really ever required to divest itself from using certain Apple GUI's back in the day (windows 2.01) ... and again, from bundling it's own writes into it's OS platform.
Facebook owns what it owns. Though a court may impose certain divestitures, Facebook is going to walk out of the court room having written it's own rules to satisfy the federal authorities.
Since roughly 30% of the value any big corporation doesn't really exist in real time, Facebook is going to divest itself from that 30% and walk away. Facebook will still own the data centers, and will charge fees accordingly for any of their use outside of the real time company ownership, just like how the Baby Bells back in the day had to pay AT&T for use of all of those millions of miles of hard lines across the United States.
My main point here is that nothing is going to happen to Facebook. It will be business as usual just as it's always been. There will be a bit of huff-n-fluff in the media and people that don't have millions of dollars will be aghast at the fine(s) imposed.
Usually by the time the federal government steps in, the damage has already been done and these companies walk away none the worse off for it.