if you look at what happened to UST, yes it was a big failure. and maybe because of this problem regulators will tighten their oversight of stablecoins in the future. this will give concern to everyone that stablecoins are not really stable and there will always be a possibility of de-peg in the future.
Regulators could do whatever they want with the coins, it will not really change anything too much. Of course it will be quite good for people to act carefully about the stablecoins because we are talking about 100+ billion dollars invested into these stablecoins, and regulators will want to protect people about those.
However, it is not based in big nations, they are based in places like Bahamas or something in order to be safe from those regulators. Meaning if USA bans it, you could still get it via Binance or something and still participate, plus we are not just from one nation, hence it will not really make too much noise for anyone neither.