Any number of crazy things can happen. Us Americans live in a country where the president declared a weeklong bank holiday and banned gold in 1933.
In 2008 the London Interbank Overnight Rate (LIBOR) went nuts as the housing crises erupted and banks had trouble finding payroll liquidity for client businesses.
But there could be a massive all-gold meteor that ironically lands on Mr. T's neck or the space aliens could show us how to turn our poop into silver using common household items.
I'm being a little silly but bank runs and emergency holidays have happened. There is no 100% safe place to put money. That's why most of us end up with a massive mess of cash, bullion, multiple bank accounts, brokerages, IRAs, Roth IRAs, 401s, 403s, Bitcoin, and moon real estate and after 7,000 pages of bank statements and 14 pots of coffee still can't figure out where all our money is or what our estate is worth.
If all this seems goofy just imagine my mom who did the "correct" thing and took all her silver dollars to the bank in the 60s. Now in hindsight she lost a lot. but there's no real way to know. As I write this my kid is playing with my collection of Franks and Bundesrepublik Deutschmarks.
As usual with economics, clear as mud. But as others have said that's why we diversify.