DeFi, generally on Ethereum, would be severely impacted from a Tether fallout. Curve’s largest pool, which is the basis for a lot of yield in other services, can be drained to zero if Tether has even a minor sustained depeg. Tether backed loans at a variety of services would likely default sending liquidation events across all the major tokens on Uniswap and Sushi. Bitcoin wouldn’t do great but it is insulated from a DeFi ecosystem collapse that would undermine Ethereum’s value.

As for regulatory risk, I think privacy coins are the biggest target.