remember that Stewart is a Canadian and that 8 Billion US dollars is approximately 2.6 Trillion Canadian loonies, that's just about enough to get him a nice 2 bedroom condo somewhere near downtown Vancouver ;)
It also raises the question of how much ownership he retains of the company and how much of this would actually be his decision (vs. his investors looking for an exit) given that they've raised a Series E round and have taken ~$340M in funding [1].
Remember that the Series E round was on a very large valuation. He surely gave up a much greater % in the early days when the company was still working on a game.
