I'm not saying that he should be barred from the surgery. It's his body and he should do what he thinks is best.
Because the team isn't on board with the surgery and it is experimental, I think they should have some recourse contractually should the outcome be unfavorable...especially if their medical resources are saying it is a bad idea. When they signed him to the contract it is unlikely any of them anticipated he would elect to have a part of his spine replaced with a piece of titanium, especially if there is a "better" option. I am not sure how one could forsee/reduce the risk of a player doing something seen as "risky" like that to their body after you make such a hefty financial investment in their future as an athlete.
I think there is a reasonable assumption that the player acts in their own best interest to keep them playing at a high level-- which is beneficial for both parties. What if, for the sake of absurd argument, there was an elective experimental eye surgery that Eichel wanted because Drs told him he'd be able to see the puck better or something, but Buffalo was like "WTF you can't be serious, Jack. This is stupid as hell". Should buffalo be strapped for 7 years with a half blind Eichel because he got a surgery that everyone who worked for the team told him was a stupid idea?
*I put better and risky in quotes because I'm not trying to imply I think I know what the best option is. I have no idea.