Purely guessing here with some random thoughts...
Many people already think we are nuts for riding. Why would your surgeon be any different?
The surgery sounds like a huge investment of talent, training, money, time, and resources from a wide variety of sources. Maybe he thinks that investment in you would be wasted by exposing yourself to the many risks we accept as riders.
If you can tilt your head up and down and to either side as well as turning your head in either direction, it still sounds like a go to me. Altering the ergonomics of the bike, getting a different bike, or altering your riding style may help.
If the surgery leaves you more fragile with a high probability of riding having an effect on the results of the surgery, then it's up to you to decide how much risk you're willing to accept. You're already doing that. It's just one more factor to consider.