I'd go one further. He loses his senior status and can never gain access to the inner workings and other members' abilities to make contingencies without their consent. The Martian Manhunter will make sure of that.The last thing I would want is to not be sure where the person who knows how to take me down was. So yeah, I would keep Batman if only to make sure that at least I know where Batman is.
But in this situation, even then I wouldn't have kicked him out. He had plans for everyone including himself. Having everyone in the league know said plans does nothing when one is mind controlled and can share the secrets with the villains.
But yeah, fuck BatGod. Keeping him watch is the only reason he's still a Leager for this.