I had the vitrectomy with the gas bubble, and did not spend much time lying prone, due to the fact that my nose got congested in that position. You can still keep the face down position sitting in the massage chair. You can also sit in a chair with your head down and not supported, but this will put strain on the neck. I spent a good bit of time lying on my side, propped up on pillows, head down with my face supported by one hand.
I think your husband can manage. It will obviously be harder with the back problem. Good luck.
It depends on what kind of surgery. A vitrectomy with a gas fill will probably require face down but some vitrectomies use silicone oil which does not. I'm not a retinal subspecialist. Discuss the situation with the retinal subspecialist.