Imagine a 1000 year old person that had segments of his brain slowly replaced bit by bit, turning him into a sort of "Theseus ship" of sentience, with no one segment being the original but there being no real specific moment in wich it "died", only lost memory and got it replaced by fresher bits.

This seems infinitely better than transhumanism, since you're constantly forgetting the past there's no moment for the existencial dread to kick in nor any fear of actually fully dying, just a constant shift