Hoping to make money by betting on Tether collapsing is like taking out insurance against the event of a combined global thermonuclear war & genocidal alien invasion of the Earth.
If you win the bet, you won't have anyone to collect from.
I suppose if Tether collapsed to the extent that it was impossible to trade it at all, you'd have a hard time buying the worthless Tether back. What happens if you're short a stock traded only on the NYSE and the stock exchange itself disbands? Or maybe the better analogue is, how do you fulfill your end of the deal as a short seller and return the shares owed to your counterparty if the company disbands in the meantime?
If you're short a company and the company goes properly bankrupt then the shares are literally worthless paper, you just throw them away.
I've been in this situation with interactive brokers and the position just disappears. (You get the profit as though you closed the position at a price of zero.) Shares of something that doesn't exist similarly don't exist. They just vanish.
They have $78B of assets, not $78T. It wouldn't rival even the smallest of national defaults. Heavy rhetoric but a bit OTT don't you think?
They also have no obligation to pay anyone a cent of their reserves. Any USDT->USD exchanges they do/claim to do are a courtesy, not a requirement.