Yeah, Ferid’s chances to survive the manga are slim, imo. Kagami said in one of his interviews that he likes happy endings and even thinks that a work of entertainment without a happy ending can’t exactly be considered entertaining, although the definition of “happy ending” varies from person to person. Ferid is established as irredeemably evil, so from that and from Kagami’s statement, I believe that such evil will be inevitably punished, although I expect it to happen only at the very end, so it’s a long road ahead.
I think the shit will be grow exponentially to some serious global scale, so much that sometime later the Progenitor Council, that already seems ineffective after all those blunders they have made (from not keeping close tabs on Saitou and subsequently allowing the first end of the world he apparently instigated to take place 8 years ago, to Crowley and Ferid easily deceiving them about Crowley’s origin and power level literally for centuries, and to Krul keeping the Hyakuya seraphs instead of getting rid of them like she was ordered to) will lose its significance completely. I’m of the opinion that eventually, Ferid will create a situation so desperate that even the strongest vampires would be scrambling to survive somehow. Yeah, as you see, I have high hopes for him as a villainXD
If you mean he would be transformed into a demon… he’s already hardly any different from a demon, and if he becomes a Cursed Gear… oh boy, he has all the chances to become the most vicious Cursed Gear in existence, one that no one at all can use because no one can stay sane after those mind games of hisX)