This is a good way to frame it. The stock market going to zero means everybody has stopped valuing companies, and presumably the companies themselves are not creating value anyone can buy into.

That puts us back to pre-industrial planet. Is that going to happen in this generation? I wouldn't worry too much about the stock market disappearing and taking all your money with it then.

Diversifying mainly means not putting all your wealth into one industry. It doesn't mean "Don't rely on stocks" or whatever.

If you only have one ship and it goes down, you go down with the ship. If you have a fleet, you can stay afloat. If you manage your fleet like a battalion, you just might win the battle. Ships won't suddenly cease to exist.