This is always the ultimate conclusion to sincere atheism. The atheist, existentialist Camus acknowledged the inevitable nihilism which atheism leads to leaves only one real philosophical question - “why continue to go on living?”
"We are going to die, and that makes us the lucky ones. Most people are never going to die because they are never going to be born. The potential people who could have been here in my place but who will in fact never see the light of day outnumber the sand grains of Sahara. Certainly those unborn ghosts include greater poets than Keats, scientists greater than Newton. We know this because the set of possible people allowed by our DNA so massively outnumbers the set of actual people. In the teeth of these stupefying odds it is you and I, in our ordinariness, that are here. We privileged few, who won the lottery of birth against all odds, how dare we whine at our inevitable return to that prior state from which the vast majority have never stirred?"
- Unweaving The Rainbow, 1998.
But Camus also realized that meaninglessness, far from engendering despair, provided the ultimate liberation. If life is meaningless, then the very purpose of living becomes to assign it whatever meaning we want!
See “The Myth of Sisyphus.”