The consequences of a 51% attack are greatly overstated. A 51% attacker can prevent new transactions from confirming, and roll back recent transactions. They can't roll back transactions that happened (roughly) longer ago than the sustained duration of the attack. They can't mint extra coins, or double-spend arbitrarily old transactions. Under 51% conditions, you need to be more careful about accepting recently-confirmed payments, similar to 1 sat/vB transactions in a full mempool today. You can still transact, you just need to be patient and careful. The value will drop, yes, but it won't go to zero unless the attacker is able to sustain the attack indefinitely.