Why is transhumanism a fantasy? Our consciousness arises from the functioning of our physical brain and if we can duplicate that functioning in a machine then we can live much, much longer than we live know.
I'm not so sure. Can you find chips that are guaranteed to last as long as a human brain lasts?
Oh, FUTURE technology, I hear the cries. Sorry, no, the direction of technology research goes in the opposite direction, towards faster, smaller and less durable. There is no reason why this should change, given that those who sell want to continue selling replacements as often as they can get away with.
Show me a computer built to last longer than a human lifespan, and I'll lift an eyebrow. Until then, it's merely a fantasy.