I believe FTX has some 10+ billion USDT on hand. That'll put a serious hole in their balance sheet. Not to mention whatever would happen to their futures insurance fund when the collateral evaporates. I'm trying to find my source for their balance sheet size, will follow up.
I'm very skeptical that FTX has 10B USDT on the balance sheet. OP here says Sam has billions of tether, which makes sense but is not enough to blow them up, and is likely in Alameda being as he says it's for trading, not in FTX.
(Of course it's possible that FTX has 10B in USDT deposits, but that belongs to their customers who would be very sad if it nuked but doesn't directly hurt FTX.)
Futures insurance fund may be an issue, yes, especially in scenarios where it shifts very rapidly. If you have math on a plausible scenario and total losses across the major markets I'd be interested in seeing it. But you'd have to be looking at several billion in losses or at over 1B directly attributable to FTX for them to go bust - they've raised over a billion and make 350M/year per recent Forbes article, so that's a lot of capital.