Either way, acquisitions this big have complex financial structures in place that would easily accommodate a payout over several years. The Roche acquisition of Genentech took more than 20 years, although the latter was already public at that time.
Depressing the stock is not the main problem of that. Insider trading is (he cannot liquidate FB stock on short notice as he has material undisclosed information pertaining to it).
He might elect to use a 10b5-1 plan (which basically empowers the broker to make the sell decision autonomously in the future based on a target price), but if you want that cash tomorrow, borrowing against the stock is more appropriate (see for example http://www.businessinsider.com/larry-ellison-has-a-10b-credi... ).
Let's assume for purpose of shareholders, I believe Zuckerburg (famously) has majority interest in voting shares.
In practice that should mean he controls who is on the board should they not vote in alignment with his preferences; however, certainly there could be other agreements/contracts the guarantee board seats here and there, that should all be available as a public company I just haven't looked.
At minimum, one would "assume" Facebook required board approval of a $1B+ acquisition.
if so, what would be the legal ramifications? I mean facebook is basically mind control for so many voters, they can push any info they want