The era of FUD on USDT for me is already done.
It's already 2023 and I will not see any FUD about the USDT depeg.
But let's just answer OP of the "what if"
My answer is the market will crash, extremely crash including Bitcoin and other altcoins.
After that, even other stablecoins for sure will get affected even USDT will only, it's because of fear that other stablecoins could be also depeg because the highest market cap stablecoin and the first stablecoin crashed.
After that, Bitcoin will recover just nothing happens as Bitcoin doesn't need stablecoin at all.