What a crappy time to have to come to terms with having no control over your loved one's actions.
I definitely agree that a non-supervised detox could be dangerous & I'd worry about that time period in between when he is "supposed" to stop drinking prior to the surgery & the surgery itself. Whether he white-knuckles through OR succumbs & sneaks a few drinks he's compromising his health while under anesthesia.
We could make the argument that as a grown man he's aware of all of this & is capable of informing his medical staff & that this is all on HIS side of the street.
OTOH, he may not be making the best decisions due to his addiction & we're talking about his health here, so it's understandable to be concerned & maybe even cross the street to talk to his doctors & inform them of his detox & see what they suggest for him following surgery. Comfort foods/tons of water/ extra vitamins/ sleep/ etc may be standard detox comforts but not easy following oral surgery. Good luck & congrats on your own sobriety!