What is missing in this discussion is the notion of finality or end, or
telos. Without having a sound philosophical anthropology, we cannot hope to assess the question of death. (Indeed, bad anthropology is at the heart of so many bad political orders. If you misunderstand the nature of Man, then the political order will be pitted against human beings in some manner, by design if not by intention. In the US, the self-interested, hyperindividualistic consumer anthropology construes human beings as selfish beasts whose highest aim in life is to consume, a degradation of the self and a degraded view of others as others become objects for consumption. Communism and socialism suffer from their own grave errors, but an eerie overlap exists between the two.)
So we must first know what it means to be human, which is to say, what the actualization of human nature consists of, actualization as the satisfaction and raison d'etre of human activity. It is the nature of a thing to seek to realize itself, to become fully the kind of thing it is. This does not necessarily involve conscious, purposeful act. Bacteria do the same, and this is by virtue of how they are organized and ordered, as well as their operation in accord with this ordering. For human beings, it is to become fully human, which, again, is the question posed: what is the end of a human being? Only in light of human nature can we determine the meaning of death, whether death is to be understood as an aberration needing a solution, or the natural terminus of human existence. If it is the former, then we might ask what, if anything, could or should be done about it. If the latter, then we must accept it as our natural end against which any resistance is not only misguided, but harmful.
To answer this question, we must first recognize that what is most essential and definitive about human beings is that we are rational animals. Our rationality is not some thing tacked on to us, but what it means to be human, and our organization, our substance, everything from the operations of the intellect, our ability to choose between alternatives freely, and our bodies, follows from this fact.
Then, we must determine what it most means for human beings as rational animals to attain finality. Classically, the highest good is to know and thus experience union with the Highest Good. But the Highest Good is infinite. Perhaps by human nature a certain finite degree of knowledge of the Highest Good suffices, but if the intellect is by its nature open to expansion by the act of the Highest Good, then it could, indefinitely, spend eternity coming to know increasingly better the Highest Good by first becoming indefinitely expanded. This would be transcendence, this expansion of the human person beyond what is merely given by nature, but which, by nature, is open to expansion by the Highest Good.
Of course, we cannot attain this condition ourselves, as we cannot engineer our own transcendence. If we could, we would already be in possession of the cause, and thus it would already be part of our nature and therefore not transcendent (the effect is, after all, virtually in the cause; you cannot give what you do not have). This makes transhumanism a fool's errand, as we can only cripple or deform humanity in our quixotic attempts to lift ourselves by our own bootstraps, unlike medicine, which only restores what is already due by nature, but is for some reason missing and in a state of defect.
Assuming this is true, then only eternal life would suffice. Anything less, merely life extension, would not change our fundamental condition, only postpone what was always inevitable. Death would remain an obstacle. But nothing in this world attains this eternal state. As I've said, technology cannot attain this end. Only the Highest Good would have this power, and thus something beyond our power to control and use. Furthermore, there is no one on this planet who can be said to have received this eternal state, at least no one walking among us that we can see. So either this eternal state is possible only after death, which means death is not non-existence but some kind of transition, or it cannot be attained. The first gives reason for at least some hope, the latter is world-weary hopelessness, an absurd condition in which Man is condemned to seek an end he cannot possibly arrive at by any means, but must seek if he is to live.