To even consider "immortal" as possible suggests someone hasn't had a lot of formal math training. Infinity is rather large. In an infinite amount of time, any possible conjunction of circumstances that could cause an immortality system to fail will happen. Talking in thousands, millions or even billions of years doesn't even need to be rounded to be basically zero when compared to eternity.
Death is a certainty. No amount of technology can change that even theoretically. We don't even have reason to be confident that the universe itself is eternal, let alone any component of it.
I don't think I am. What would the path be to thinking it is possible? In the best case scenario where everything we know about physics turns out to be wrong and the universe miraculously allows complex eternal patterns to form it'd still eventually end up as some entity that thought a completely different way, had a completely different form, and has a very limited understanding of the concept of "what I am" because it'd have to keep changing parts of itself due to unexpected circumstances. It'd be a ship of Thesius to the point where there wasn't even a memory of what a ship was any more. A severe Alzheimers patient would be the same person they always have been compared to what an eternity of change would bring.
If that is immortality then we may as well call it a tautology and say we're already immortal. None of the things that make people who they are need to be preserved to achieve it so we're realistically already there.
Living an absurdly long time I can get behind. Billions of years, trillions of years, unimaginable numbers of years, sure. That could happen. But immortality isn't an option, everything eventually dies off unless we play semantic games where there aren't any properties of the thing that need to be preserved. And maybe even reality has an expiration date for all we know, which would render the whole project moot.
If we look at afterlife beliefs-and their secular substitutes such as life extension, cryonics, mind uploading, simulationism, quantum immortality-I don’t think they all have the same motivation-two people may adopt the same belief with different psychological motivations.
For some people, the idea that their present conscious moment might eventually be left permanently without any future extension is terrifying-but provided that doesn’t happen, they might be neutral (or even positive) about the prospect of the contents of that consciousness eventually becoming so radically transformed that it becomes a completely different person, or even something which transcends human notions of personhood, albeit ultimately still continuous with the person they are now. For other people, that prospect is terrifying. It really depends on what one is most attached to - the mere continuation of one’s own consciousness, or its distinctive contents that makes you you.
Death is a certainty. No amount of technology can change that even theoretically. We don't even have reason to be confident that the universe itself is eternal, let alone any component of it.