One relevant philosopher not mentioned here is [Henri Bergson](https://en.wikipedia.org/wiki/Henri_Bergson), whose critique of the concept of nonbeing distinguished him from the existentialists he spawned. I believe his argument was that nonbeing is a complication of the idea of being (nonbeing = being + negation), rather than a truly distinct and opposed concept, and that philosophical questions having to do with nonbeing were just poorly stated problems.