This makes it clear that we must be careful to distinguish between the ledger (a conceptual spreadsheet keeping track of who owns what percentage of the economic community known as "the Bitcoin ecosystem" and later perhaps just "the global economy") and the protocol for updating that ledger.
We're back to this silly idea of separating the currency from from the blockchain. You can't, they are one in the same.
This "ledger" rhetoric is a paraphrase of the false idea they are separable.
The system is the blockchain is the currency is the protocol is the ledger.
Yes you could. Not to say the currency can run without a blockchain. Of course it can't.
But you did not address the essence of ZB's argument which is that monoculture in currency is absolutely desirable. We don't want multiple ledgers of ownership where different, conflicting stakes are attributed to the same persons.
This ledger cannot "economically" fail, only the protocol updating it. If that happens, we could still "transfer" a picture of the ledger (who owns what) to a new protocol that will update it. So yes, if the blockchain fail, we could, theoretically, seperate the currency (ledger) and "attach" it to a new chain.