I think Tether can get away with less than 100% collateralization. At the current market cap of 82bn, even if they are only 20% collateralized, it takes 16.4bn one way movement to deplete their reserve. Is that likely event? Guess it depends, but I think market makers would be more willing to backstop them than UST shitshow. UST has "death spiral" structure that makes MMs less willing to backstop them once it goes on a path, which is exactly what hedge funds attacked against these past few days.