I dont think they can just make a new arm for him. It's strongly implied that he's fusing with Barbatos.
Given what we know of the history of the frames, the Alaya system, and Ein, I feel this is likely the case. Not all frames are created equal and once you start to lose yourself in one, you can't just switch to another. The frames were hated and feared for a reason, and "consuming" their pilots is as good as any.
Given what we know of the history of the frames, the Alaya system, and Ein, I feel this is likely the case. Not all frames are created equal and once you start to lose yourself in one, you can't just switch to another. The frames were hated and feared for a reason, and "consuming" their pilots is as good as any.