The real question is, would Stewart B. take the offer?
Anyone who cares about their product knows a sale to MS is a death knell for innovation. Becoming a hit like Slack is such a rare opportunity. I mean, why are you in this business if not for a chance to build a transformative platform? Which is what Slack has right now, a chance.
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.
Anyone who cares about their product knows a sale to MS is a death knell for innovation. Becoming a hit like Slack is such a rare opportunity. I mean, why are you in this business if not for a chance to build a transformative platform? Which is what Slack has right now, a chance.