I gave it more thought, and I think that is highly unlikely. This is what would happen:
Tether starts to drop, let's say it is at 90 cents. Tether holders get scares and start to buy just about anything. That causes a short term rally, I would say a few days tops. (maybe just a few hours, depends on how fast the exchanges act) Somebody has to be getting all those unwanted Tethers and that is the exchanges. So they quickly realize that they are the ones ending up holding the Tether bag and will suspend Tether trading. Probably other stable coins get dumped too for at least a while. If another stable coin can take up Tether's current role that is still to be seen.
So a short term rally and suspension of Tether trading what I see.
You might be correct that exchanges will halt Tether trading, but that's cefi
defi platforms, i.e. dexes will not halt until liquidity is drained from all liquidity pools
And there are the other $60 Billion worth of other stablecoins, USDC, BUSD, USDP, GUSD that will be used to buy bitcoins and other crypto assets.... and those stablecoins are issued by US companies