On the keeping Adel alive business: can they actually kill her without releasing her from that seal? I mean, that seal managed to prevent the vacuum of space, along with the lack of oxygen, from killing her. If this is true, then he didn't kill her because, in removing the seal, there was the probability that she could free herself and return.
Also, the lack of a suitable successor to her power is perfectly plausible bet. I am almost 100% sure that a sorceress' power is transferred whether the sorceress wants it or not, based on how Rinoa received Edea's power. And, considering the consequences if they got it wrong, then perhaps it would be best to leave her in space indefinitely. One less sorceress to worry about.
R=U is a bit far fetched for me. If you put two pictures of them next to each other, there is some resemblance. But, for them to be the same person, they have to look nearly identical. You cannot find such a photo. You may be able to find a transition of the two faces on Youtube, but that is an optical trick. Find me two photos next to each other, and we'll talk.