What is failure specifically? USDT (despite it's shadiness) trades at 1USDT:1$ on pretty much all exchanges and you can short it if you truly believe it'll flop anytime soon.
https://bitfinexed.medium.com/tether-is-setting-a-new-standa...
If you truly believe what you say, then you should definitely consider shorting it, if you're right you'll make a lot of money.
However I'm very interested in the idea of shorting a "stable"coin. Who would possibly enter into this contract for an asset that has an upside of zero and a (potential, long-term, depending on your bearishness) downside of 100%?
In any case, with the strong likelihood Tether themselves are effectively shorting it by selling it unsecured by any real assets it would be a tough market to get in on.
You have to borrow it to short it, so there's a 1-3% APY cost associated with shorting it. You have to calculate the tradeoff of the likelihood of it going to 0 within the next couple of years vs the cost of borrowing USDT to short it.
Say you short 1M$ worth of Tether, it goes belly up within 4 years, it cost you like ~40k$ to short it, but your upside is 1M$. If it never actually fails because the market is irrational or by some miracle Tether was doing the right thing, then your cost depends on when you close your position. It's a relatively cheap way of making lots of money depending on your conviction on Tether's likelihood to fail.