Hide behind the fighter, she should still be able to hack it apart with her enchantment dead. Does he just knock out your items or is it a walking antimagic field? If not just cast some ethereal type spell and cast magic missile.
Let me ask in another way how many ways are there to come out when your are grappled by a Balhannoth
Well, I know one for sure: dead!
Other than that, if you are already grappling it seems pretty tough for a wizard to get out of such a tite spot. No strenght, little chance for getting your casting through, leaves only the option for a truely great 'escape artist' check!