What was unsustainable was the will to calmly ignore 19 billion dollars sitting on the table. I would certainly fail that test.
I wonder if they considered a legal structure which would tie their hands, precisely to prevent such a thing. Long before they got so big, I mean. Would that be possible?
I would likely also accept that deal. That's a lot of society's resources you get to direct to solve other problems you care about, and also have plenty left over to, you know, build another open source chat app (once contracts expire—https://www.wired.com/story/signal-foundation-whatsapp-brian...).