This is a good question for discussing how metaphors and other figures of speech function in using language to convey ideas. As with any complex organism like mammals, there is an important, even (as the word implies) a vital connection between blood circulation and brainwave function, and whatever criteria you use to determine the termination of life, it is an irreversible process. When we say that a cat has nine lives, we are actually referring to its agility, it's ability to cushion a fall with its limbs, its ability to crawl through small spaces,etc., so that they give an appearance of surviving deadly experiences. Language "flattens" this idea, here with the soft verb "have". Today the saying has achieved "cliche" status, and fills a space in an utterance without demanding fresh expression.
its a saying that cats can get out of trouble
.... What do you think?