why? a lot of the market already trusts stablecoins like PAX and USDC a lot more than USDT. they're issued by regulated/licensed companies. plus, if the market starts dumping their stablecoins below their redeemable value, big whales will just arbitrage them back to $1, because free money.
If their bank accounts are frozen by the authorities, then it may not be possible (at least in the immediate term) to convert USDT to USD at 1:1 ratio. Obviously the risk is there for all the stablecoins, because they need bank accounts to store their fiat cash reserves. I don't think that any of them would chose to store the money in the form of banknotes and coins (even if they do so, the risk of confiscation is there). And a few days back, we saw how easy was it for the banks to shut down the account of the former president of the United States. Given that, do you really think it will be difficult for them to either freeze or shut down the bank account of any of these stablecoin foundations?