I believe Bret entered facebook via the acquisition of FriendFeed and any millions hes making out of Facebook likely came via that and any golden parachute he had (which I'm sure he hit considering he's been there 3 years)
Also a lot of C level execs work on different vesting schedule and get allocated shares as bonuses. The whole point being this question is largely moot on a lot of levels any stock left on the table is probably a very small portion of what he was bound to make on the IPO via a standard option vesting.
I couldn't think of any scenario - unless there was something profoundly personal/family oriented going on - where someone in his position would leave before they have vested.
I had the good fortune of joining Sun the day the Monday after they went public. There were certainly people who left 180 days later, even though they had unvested pre-IPO stock, because the return on their vested stock was 'enough' for the next stage of their life.
There was also a clue in their S-1 [1] where his name is not included in the 'executive compensation' section, generally that is a sign that either he won't be continuing on with the company going forward (likely case) or that if he quit it would not materially affect the company (hence not of interest in the prospectus)
Given that he's been there 3 years out of four, has a C level position, and all of the other C level jobs have multiple millions of shares, lets give him a 'lowball' grant of 4M shares. So 3/4 are vested and that is 3M shares. So FB is currently $30/share but lets say he sells all 3M and pays 50% in taxes. Lets be even more pessimistic and say that his sale pushes the price down to $25, that is 1.5M shares @ $25 that he pockets free and clear. So $37.5M in the bank. Perhaps he did this math and said, "You know, I've got lots of things I want to do and that chunk of money would give me the freedom to do it until I die."
You would be very very surprised at how common this is. Lots of people leave 50% thru vesting; it can be remarkably demoralizing if you're of the entrepreneurial mindset to work for four years in a large organization.
Not if he negotiated properly coming in, which I suspect he did given this quote: “I had always been upfront with Mark that I eventually wanted to do another start-up.” If he was upfront, then that means before he came on board. He probably negotiated a condition that if he stayed through the IPO that xyz would happen (vesting, whatever else). He carried out his end of the deal, therefore xyz happend. Everybody wins (except those who bought FB on the IPO (or on one of its first 12 days as a public company).
Because vesting periods are usually four years and he joined Facebook three years ago, he's giving up at most 1/4 of his stock related compensation. Because Taylor joined Facebook through an acquisition, it's possible that his vesting is shorter than four years.
He probably has restricted stock units and common stock with a buyback provision. As far as I know, Facebook stopped granting options before Taylor joined Facebook.
