Debatable whether the feds would go after the competing stablecoins, but depending on the logic for the prosecutions/seizures, there are outcomes where they're economically inviable.

e.g. If Tether gets shut down because of fraudulent misuse of reserves, then the government might be OK with some aboveboard execution. If on the other hand they get shut down for money laundering via tether, well, stablecoins exist to enable that, and if they can't enable that they likely don't have a use case large enough to support the engineering/operational teams required to run them.