LogFAQs > #972830741

Square is aware of the theory, so they can poke fun at it. The Ultimania confirms it isn't real.

People misunderstood the idea that sorceresses can't die without passing on their powers, as if that makes them immortal. Sorceresses have normal lifespans. They'll involuntarily pass on their powers if they're on the verge of death (see Ultimecia in the ending).