Have an intervention with him. Get all your guildies together in discord and confront him, tell him that he needs to relinquish guild ownership or you’re all going to plaster his name and reform.
I’d give him a chance to redeem himself if he was such an integral part of the guild since classic and kept it going, it sounds like he needs you guys more than you need him and it’s become a responsibility to protect him from the outside world.