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.
So looks like on legal paper Tether doesn't guarantee it's 1:1 backed by USD.
Now it looks like collapse of Tether is more likely than not.
Such toxic terms of service. Basically it prevents you from taking legal actions against them if Tether collapses and causes you heavy loss. Even if you sue them you'll likely lose in court.
Dirty but "standard" business practice.