Things exist contextually. Did the French Monarchy exist in the 1700s? Absolutely. Does it exist now? Absolutely not. Its existence depends on the time frame. It’s perfectly fine to define existence conditionally rather than absolutely. That’s how our brains work and it won’t change reality if you’re wrong.
The question “can nothingness exist” is a semantic question with no substance. You have to define what the terms mean first, nothingness and existence, once you do, answering the question is straightforward.
One way the world might not exist would be if you’re thinking in the Buddhist context, where nothing exists and everything is impermanent. Meditate on that long enough and you’ll become enlightened.