I don't think it's that cut and dry. They perform the stabilization surgery either for cases where the injury is worse than anticipated (broken vertebrae, herniations, spinal cord damage) and needs added support. This is the most common reason. The 2nd reason they do the surgery is to help it heal quicker. In either case, he had metal or something else inserted into his spine and it will take time just for that to heal. Of course, we all hope the reason for the surgery is the 2nd reason but that certainly has not been stated publicly by anyone.
I had this injury back in 1993 in a car accident and had 2 broken vertebrae. They were stable so I didn't need surgery but I had to wear a back brace for three months. Again, hopefully, he had the surgery to speed up that 90 day process but I think it is quite a stretch to think he might come back this year. If he did, it would be well into the playoffs.