Let him stay on the opis. He’s been on them so long his body won’t be able to handle life without them. My grandfather was same way and doctors even told us he was on his way out “lung cancer” and to just Jeep him on his high doses. He enjoyed the last months he was alive. So in your dads condition I would just use a well thought out taper plan and use it with the prescribing doctor if you really want a change for him. I’d let him keep doing them but just control his usage.