I tend to think the opposite, that large cryptocurrencies are likely to always be worth more than $0, even if some black swan like a 51% attack were to happen.

I tend to think the opposite, that large cryptocurrencies are likely to always be worth more than $0, even if some black swan like a 51% attack were to happen. After all, "worth" is subjective, and the behavioral guarantees cryptocurrencies make (notwithstanding black swans) are attractive in assets.