RONOUNCEMENTS disallowing a self-recognizable existence beyond corporeal dissolution usually begin with a purely materialistic world view, denying the reality of anything that is neither discernible nor supported by other empirical evidence.
This would also exclude so-called supernatural manifestations, as well as any chance of there being in place some kind of incorruptible soul-like vehicle for the purpose of maintaining our awareness when our brain cells disintegrate, or for that matter a construct for any kind of afterlife.
Compare time before conception to that after death. Since few of us claim to (and likely none of us actually) remember any conscious existence prior to this carnation, it seems reasonable that the eternity following our earthly demise will be the same, a forever of nothingness.
This argument is weakened somewhat when we take into consideration the differing intrinsic nature of birth and death, congruent with the arrow of time—
Generally, from unaware potentialities at conception, growing in the womb and leaving it, evolving to maturity, and eventually declining precipitously or even suddenly, to— importantly— perishing having been cognizant of being (except in the undeveloped), which we were not when we were conceived.
Yet the fact that there’s been a time in the past when we’ve not existed in our present identities doesn’t bode well for assurance that an eventual return to such a state is out of the question.
Since the universe does not appear to be well-filled, much less overwhelmed, by extant living entities multiplying unchecked, there must be a means by which this process is mitigated, and termination at time of death seems the most likely—
Although not only can we see very little of this our universe, there might be other universes, or even other planes of existence, which are totally imperceptible, at least at present.
If, cognizant of the mystery and non-inevitability of creation, we view whatever life we are given (no matter how brief) as a gift, no more would we expect immortality than we would expect a person who had just given us ten dollars to hand over a trillion.
One problem with this is that it tries to anthropomorphize a source of all being that must be inconceivably nonhuman.