Regarding Elidibus and his hypothetical demise. I don't think it'll be as simple as killing the head honcho. The faction has been manipulating events for millennia and every oneof them, even those born of sundered souls, likely has the goal of reviving Zodiark and un-sundering the world. As it stands unless Zodiark is dealt with here and now, killing Elidibus won't stop the rest of the Convilcation from being a threat. It would still weaken them however so it isn't totally useless.