For SP500 to fail - means that the top 500 US companies need to fail.
We're talking here about Google, Microsoft, Apple, Tesla, Amazon, Nike, Ford, GE, JPMorgan, J&J, Coca Cola, Pepsi, McD, Walmart, Boeing, Goldman Sachs, VISA, MasterCard...
(full list in here ->
List of S&P 500 companies - Wikipedia )
Now, some of these might fail (and will get removed from index), or all of them can have a bad year, but if they all of them failing altogether is simply not possible
"it is easier to imagine the end of the world than to imagine the end of capitalism"
So if these are gone - the world is gone!
About crypto - if Thether is gone - crypto is gone. If Bitcoin is gone - crypto is gone. If "trust in crypto" is gone - crypto is gone. If Binance is gone - crypto is gone.
And people will still use their Visa cards to buy at Walmart and burgers at McD and will drive Ford or Tesla and will drink Coca Cola. And S&P500 will prevail.