"Death is rest for the soul".
Even to an atheist, the possibility of living forever after everything you've known and seen has passed on is equally terrifying.
What do we fear more:
Experiencing Joy/Pleasure but the inevitability of all of it ending?
Or:
Going on forever but never again experiencing joy or pleasure (the inevitable truth would hit one who is immortal eventually, assuming they don't otherwise go insane).
Since the former is obviously what exists in reality, we worry about it more.
The second option is purely hypothetical, but pretending it's true for even a moment, is so far beyond our comprehension it becomes equally frightening.
So with all that in mine, from a purely secular point of view: There is no decisive answer.
OT: I will die eventually; but until then I must live, and I've chosen to live so I can try to understand at least some infinitely tiny fraction of how our universe works.