Not to pick nits but there's a good chance he would have to liquidate some stock in order to do that, which if done improperly, would have the effect of depressing the FB stock price, thus affecting the board and all the other FB investors.
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... ).