It is true that we cannot imagine the state of being dead, because not experiencing is not something we can experience. But that does not mean non-existence is “literally inconceivable”. In fact, it’s very easy: just think of the world in 1066, or any time before your birth. Imagining being dead is impossible, conceiving your own non-existence is not, and hence there is no mortality paradox to resolve.
Review of Immortality: The Quest to Live Forever and How It Drives Civilisation by Stephen Cave in the FT Weekend (31 March/1 April)