GAW: I asked my father that. He said that one of the rules of nature that HKBH set up was that someone who eats from the Eitz Hachayim will live forever. Thus, even though He can abrogate that, He usually limits himself to the laws of nature that he set up.
WADR, that really makes no sense. If Hashem is willing to make the murderer walk under the ladder at the same time the Shogeg is going up, he can arrange that the eater trip on a rock and shatter into a gazillion pieces, or have his head chopped off, or fall into a pot of boiling water, etc. Unless you want to say that eating from the Eitz HaChaim changed the physical nature of a person (less biologic, more like a malach), then that doesn’t make any sense to me.