Let's say you can rebuild telomeres while curing cancer and keeping arterial walls healthy, and even prevent the physical aspects of dementia or Alzheimer's. Who's to say that an immortal human can retain consciousness, let alone sanity? What would be the psychology of an ancient being? What happens to its memories, how could it recall anything from centuries past? And, as sometimes explored horror and science fiction, how would such a creature retain its humanity rather than becoming a hedonistic, nihilistic misanthrope that considers itself beyond petty morality?