Quote Originally Posted by Skyblade
Similarly, when a sorceress dies, their powers are recycled to a new vessel (albeit one already alive). It's not a case of the powers keeping the sorceress alive, it's a case of as soon as the sorceress dies, her powers, like her life energy, are recycled into the system automatically. A sorceress can choose to give up her powers before death, but can not die without passing her powers on, for death itself will pass the powers on. When Edea meets Ultimecia, she is saying that she is looking for someone to pass her powers on to so that she can "die in peace". Perhaps death without passing on ones powers first is possible, but not very pleasant.
Well, that's a fine theory, but has no backing in the game. In the game we never see the sorceress powers being recycled in such a way, we only see dying sorceresses passing on their powers before dying.

Quote Originally Posted by Skyblade
In any event, since the preservation of life by not passing on powers is a direct result of being a Sorceress, I would say that the Ultimania stating that a Sorceress's lifespan is the same as a normal person's rules that possibility out.
I disagree. Same lifespan only implies aging and susceptibility to death by old age, but doesn't contradict the fact that to fully die (even by old age) they have to give up their powers. And as I said above, that's all we ever see. Sorceresses who have been critically wounded giving away their powers and then dying. We never see a sorceress dying and then some time later someone becoming a sorceress completely randomly.

Also, there is no need to keep Adel alive indefinitely. Laguna knew full well that Adel was not the only sorceress: He knew Edea personally after all, and never sought out to seal her away. He only tried to seal away Rinoa because Ultimecia had the ability to possess her. Adel was the one that they were fighting, and it seems to me that the seal was just to stop the threat from Adel herself, not to stop the power of the sorceress in general.
Obviously they weren't trying to stop sorceresses in general, but they probably thought it would be better if no one inherited Adel's powers, because of how extremely powerful they were. Thus it would make perfect sense to keep her alive indefinitely assuming that they couldn't kill her without the powers being passed on.