I doubt very much that the GMC will take away someone's means of earning a living for horrible comments on social media.
If he was a teacher he'd have been out on his ear years ago, after the first incident. Professional standards. 'Means of earning a living' is irrelevant if you've demonstrated you're manifestly unfit for the responsibility of a profession. He will have signed a code of conduct.
I've been wondering for years what it is he has over them that they've let him bumble on like this.