I'm a bit of a finance noob; is there any practical way to enter a long-term short position on usdt that would actually be redeemable if the Bitcoin ecosystem were to collapse after its downfall?
1) Find someone you know and trust who owns enough USDT.
2) Borrow their USDT, then immediately sell them for USD.
3) Pay some fee over time for the loan, and then have the contract expire at some point.
You would need some kind of contract for the fees and end condition, but it could just be an email that you agree to. If you don't know and trust any cryptofans, then no, there isn't a good way.