Glad to hear your husband is healing from his surgery.
I can't speak to your husband's condition specifically, but if the airbag deploys in an accident (and assuming your husband is of average stature and is not seated too close to the steering wheel), the air bag is going to be fully deployed before your husband even begins to move forward from the impact.
Furthermore, the seat belt is the primary means of restraining the passenger in a frontal impact. Personally, I'd be FAR more concerned with the damage a seat belt could do restraining his torso than what the airbag (which is designed to catch his face, not his torso).
If your husband was to move far enough forward in an accident that the airbag was going to contact his torso, he'd be in danger of hitting the steering wheel. I'm no expert, but I'm quite sure the steering wheel would do much more damage than the air bag would.
Now, were your husband thrown forward before the air bag deployed, I could certainly see the potential for life-threatening injuries, but that would go for anyone in that position when it deploys, not just your husband.
I'm not saying that there's never a reason to deactivate the air bags; I'm just saying that there needs to be some pretty compelling reason for it based on facts, not simple fear of what *might* happen. Your husband could just as easily sustain the same or more trauma in the same accident without an air bag deploying. In the type of accident severe enough to cause airbag deployment, the seat belt alone is going to cause issues.