I don't think anything will actually happen if you don't feed Gale magic items. Also if it will you making a Wizard wouldn't really help, Gale is still gonna need food to not go bad whether he's in your party or not.
If you're focussed on power though Gale is one of the few characters whose build isn't all over the shop. Right now even if you give Gale every single item he can eat immediately he's still a much, much, much stronger option than Shadowheart is. If you want the best party you want Gale in it and your character probably wants to be either a Cleric or a second Wizard. That or just build a custom party but that's almost always the optimal route from a power perspective.
