Did they take a wire transfer for $10bn in cash, now sitting in their bank account? Or did they get a promise of various funding over N years, subject to milestones, conditions, in a variety of media including cash, Azure credits, loan lines etc.

I'd imagine the latter, and that it can be easily yanked away.

No, that's not it; relationships play gigantic roles in large deals.

Besides, even if you had an outstanding contract for $10bn, a judge would not pull a "well technically, you did say <X> even though that's absurd, so they get all the money and you get nothing."

Depends what you mean. Legally they might be in the clear but guarantee when you fuck around with billions of other people's money, it gets more complicated that that.