Nothing is guaranteed, but unless you can somehow influence the probability of leaving, then waiting for it to occur seems rather premature.
[Even those with "new" memories have only that. Memories are not proof when they can so easily be tampered with.]
Death is only unnatural if the being is never meant to die. Otherwise it is merely caused by external or internal forces. An illness caused by a genetic disorder is as unnatural as a knife to the heart. Neither are meant to happen.