At least in all these years of trading in the crypto market, you know it's not dependent on one coin, so I am sure even USDT's fall will have some impact on investors but not the whole market. And also, USDC and USDT are fine. There is a lot of fud out there; USDT did a lot of sketchy things, but I will say USDT has a bigger market cap than USDC. There are a lot of people trying to take out your USDT, and maybe in the future it dies, but right now I don't think it's that big of a deal. I think a lot of it is a fud. But what I will say is that you can't short the market without usdt on the platforms that I use, so I am cool with holding usdt right now. In the future, that might change, but yeah, just don't get caught in the fud.
Not the "whole market"? Nearly every cryptocurrency has a USDT trading pair. I'm pretty sure a USDT crash will have long-lasting repercussions on the crypto market. Such an event will cause huge distrust among mainstream investors and traders alike. USDT has been holding well so far, but it's not guaranteed to last forever.
It's advised to cash out to Fiat (USD) whenever possible. No one knows when "the time bomb" will explode. Just avoid putting all of your life savings into USDT, and there should be nothing to worry about.