"Sure. But where will the cash go? If the lenders are also at risk, what sort of investment does that leave you? If all assets are skyrocketing and subject to crash, where is safety?"
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Please don't take the following as anything more than the idle thoughts and musings of one individual:

That depends on how apocalyptic you want to plan for. Putting the "end of the world" senecios aside (and while not a "prepper", I've mad a few provisions for that eventuality), it depends on how things roll out.

Possible scenarios:

Liquidity crisis in the US dollar:
If this causes a pulling of US funds by the carry-trade, a decrease in the value of the US dollar coupled with an increase in the value of gold and currencies of low-population countries with substantial natural resources (Canada, Australia, Brazil, for example).
US equities will drop precipitously and drag down the foreign markets (though the foreign stock prices drops will be partially supported in terms of USD by currency translation differential. Interest rates on US bonds will depend on whether they are perceived as safe and the amount of currency flowing into them. Real estate will tend to drop as leverage dries up and illiquidity (and drop in revenue of commercial property) is deemed a negative.
We lived through this in 2008.

US Stock market crash:
Less extreme than the above, but more or less the same pressures. This will not necessarily affect the US dollar to the same extremity, and therefore, a commensurate drop in foreign markets will not be abated by currency ratio shifts. These used to take place separated by a few years to a decade, but the Fed has financially engineered them away between the Great Recession and the COVID crash.

Black Swans:
Well, if wee could predict them, they wouldn't be called that:-)
My opinion is that, at some point or other, for some reason or other, cryptocurrencies will have a dramatic issue - which will snowball into other markets around the world.

So, what to do?
The following is not optimal "investing" in the same context that buying a fire extinguisher or an insurance policy is an expense - until you need them.
Physical gold (not to be confused with "paper" gold) is not a good investment for me (regardless of it's rise in price). It has to be safely stored, etc., etc. and would only be sold in time of extremis - such as if the currency became worthless. To me, keeping 1%-2% of "liquid" net worth in this and similar easily portable, universally valuable stuff makes sense. Owning foreign equities, in their native currencies, provides a stream of income in foreign currencies (much as I hate them, Interactive Brokers is the best shop to use for this purpose). Foreign bank accounts are legal, as long as filing procedures with the federal government are complied with (and can provide "targets" for bank wires if desired).

In essence, cash is king. Stocks sold can always bought back. While the market can't easily be "timed", as Warren Buffest seems to feel, having a pile of currency to re-deploy can reward the patient investor.

Real estate, while providing a long-term good investment, especially in times of duress, can be far from liquid.

Jeff