The slave provides an ERROR response. if the master always chooses to complete the remaining transfer, is the two-cycle response necessary?
Could the slave perform one cycle response of hready=1 and hresp=error?
No, because the slave doesn't know that the master might continue with the next transfer.
The protocol describes the behaviour that must be implemented so that the master can choose to cancel the next indicated transfer. There is no "If your master doesn't..." option.