One might imagine the devastation of the effect that Tether can possibly bring by just taking a closer look at the BTC trading graphics/charts:
https://www.coingecko.com/en/coins/bitcoin/trading_exchanges#panel 33.3% of the trade will be the mere minimum that will be affected, and does yet not take into account the USD and Bitfinex (which are both tied to USDT in some sort) and the subsequent decline of as well Ethereum:
https://www.coingecko.com/en/coins/ethereum/trading_exchanges#panelEthereum will be crippled if USDT fails, because not only is USDT entwined in 24.9% of all Ethereum trades, the effect is complementary to USDT affecting the underlying BTC price as well. ETH/BTC will drastically alter when a run from tokens>eth>btc>fiat starts. Most ERC20 tokens might lose up most if not all their current value. Actually this drain of value from ERC20 tokens has been going on for some time already, very slowly, and with a subtle price pump now and then for the more "popular" tokens, to keep people believing in those ridiculous projects.
If you are currently investing in crypto and the only way to cash out is through Bitfinex (USD/USDT), it might be wise to reconsider the situation you are in, again. That exchange is the first one where things will start to fall apart if people make a run for their money. Remember how in real life even a small and seemingly insignificant bank could topple entire societies and economies worldwide some years ago? And remember that in crypto there are no rules!
These people that tell others to have good faith and that things are 100% well-organized, without any motivation to pursuit a more adequate answer, they are the same people that thrive in the absence of rules as always, namely idiots (the ones unintentional bringing harm to others) and criminals/mafia (the ones intentionally not caring for others being harmed).