I'm afraid that without these diodes we may surpass the +-1.5v differential
mode input voltage at the absolute maximum ratings in an unpowered state.
The 4898 doesn’t have back-to-back diodes across the inputs.
The absolute maximum differential voltage of 1.5 V across the inputs is valid
only when the supplies are connected and active. With the supplies floating and
a differential voltage is applied between the two input terminals, current
begins to flow when the differential voltage reaches 0.7 V and reaches about 15
mA when the differential voltage is 1.5 V.
To protect the device from damage in an unpowered state, limit the differential
voltage to 0.7 V. One method to do this is realized by back-to-back diodes
across the input terminals. To ensure stability during normal operation low
capacitance diodes are needed.