I would get the cleaning and use the antibiotics this time, just to satisfy everyone associated with it. He can probably get the cleaning appointment separately earlier than the regular one. If the regular appointment shows he needs work, it must be done ASAP, preferrably at that appointment.
There is no use in pointing out that over 50 years of evidence reviewed by representatives of the AHA and ACC show no evidence that the single antibiotic predose works at all. People want to believe in the magic, and physicians like to evoke that magic aura to help make people to believe they're being taken care of, or just to cover themselves if someone does get IE. I've typed my fingers blue on this topic. Taking them once isn't likely to do your hubby damage, and it will hold the wolves at bay in this short time before the surgery.
I've had the surgery twice, and I haven't taken the premeds for years (they've caused other troubles for me). I know from the medical community's own experience that if I do ever get infective endocarditis, it would not have helped to take the premeds, so I am content.
But this isn't the time to draw this line in the sand. He may need the dental work and he does need the surgery. It's just not a good time to be at odds with anyone in the medical fields who might affect his surgery timeline, just in case they're behind the times on this one issue. Get him to eat yogurt for a few days afterwards.
Best wishes,