At the end of the day tether will still exists and remain at $1 even if it is a fractional reserve rather than 1:1 . Heck the money in our banks are fractional reserves too but that does not stop everyone from mass panicking and withdrawing.
I think @mt55 is making a fair point. In real practice nothing is can be trusted even if its legitimacy stands momentarily but because there are no or very few options left people still rely on them because that's the best there is. However, one would be wrong to think that there are 100% no drawbacks, hacking nowadays can bring companies to its brinks within matter of seconds. So it is best to remain skeptical and vigilant at all times as things can change very quickly.