Tax havens aren't immune to economic disaster though. If the US dollar becomes worthless, then it doesn't matter how many dollars you have in your offshore bank account. Ditto if you're storing wealth as equities or bonds. Real estate value will collapse if tenants can't pay rent or if the local government decides to confiscate land.

I suppose that you could keep gold or bitcoin wallets in a vault, but then it actually belongs to the vault guards, not to you.

Basically you need a collapse that's bad enough to shrink asset prices but not bad enough to break the social contact.