I'd just risk it. I'm sure they'll be able to find something he'll eat. If not, grab him something later or he only eats dessert.
I have three teen boys and we had the opposite problem. When they were still young enough for the kids' menu, they wouldn't want anything from the kids' menu and would insist on something tastier from the adult menu. It made eating out expensive, but I didn't want to discourage their adventurous, healthy, and varied food intertest with bland kid menu offerings. When the younger two were really small, we could get away with ordering one adult meal for them to split, but many places don;t allow this. Cinderella's Royal Table made us pay extra to split.
I have three teen boys and we had the opposite problem. When they were still young enough for the kids' menu, they wouldn't want anything from the kids' menu and would insist on something tastier from the adult menu. It made eating out expensive, but I didn't want to discourage their adventurous, healthy, and varied food intertest with bland kid menu offerings. When the younger two were really small, we could get away with ordering one adult meal for them to split, but many places don;t allow this. Cinderella's Royal Table made us pay extra to split.