USD will never become worthless as long as there are still people who want to live in the US and I tell you, there are plenty.

At least not physical USD notes. I am not sure about the banks.

USDT is a lot different story...

BTC's value is whatever you believe it is.

Do you believe btc's value is $12k because some exchange tells you?

BTC's real value for you is the price that'd make you cash em all out.

Nothing else. From which price would you cash out? $100k? That means your price is $100k for a coin.