Can anyone tell what are the guarantees, if any, that Tether won't switch to fractional reserves?
From the Tether Terms of Service (updated in January):
No Representations & Warranties by Tether: Tether makes no representations, warranties, or guarantees to you of any kind. The Site and the Services are offered strictly on an as-is, where-is basis and, without limiting the generality of the foregoing, are offered without any representation as to merchantability or fitness for any particular purpose.