According to the video I linked below the cut, a mind flayer option for Gale was planned, but eventually discarded (it doesn't even have voice acting, it's at 24:30 ish). It would have required him to be super eager to get that Crown, so the opposite of what you suggested.
You can blow up Gale without turning anyone into a mind flayer, if you have previously accepted the special gummy worm from the Emperor and have it in your inventory when talking to Orpheus. He will accept that as insurance. Personally, I am more than content to make Orpheus bite the shrimp, big heroic prince can do the big heroic thing. Thanks.
Thirdly, Gale has an option to redeem himself that does not require him to blow up, it's his orb-free human ending. Giving Mystra the Crown is a compromise that she agrees to and that comes with her forgiveness, she may or may not make him her Chosen again in this version too.
It would be cool if you could ask Lae'zel why she doesn't want to volunteer though.
