What happens to an ETF if the currency it is denominated in goes bust (hyperinflates or dies off in another uncontrolled way)?

For example, people saving/investing for retirement in ETFs on European exchanges. Securities are denominated in €, but what if € doesn’t survive the 10/20/30/40y until their retirement?

Also:

1. Is there a difference between stocks and ETFs? My layman thinking is, a stock is a share, until the company survives, you can sell the share in another currency. Is this true? What about ETFs?

2. What if the specific ETF is € only and has no “counterparty” in another currency? Are you entitled to a % of the ETFs shares/stocks, or does your investment “die” together with the ETF if the currency goes bust?