That's not what I meant, I meant if all organic life that produces oxygen disappeared.
Photosynthesis is generally so slow at it's job that the current oxygen levels were only built up over hundreds of millions of years. Furthermore, Rubisco, a key enzyme in photosynthesis, surprisingly, is slow and not very good at distinguishing oxygen from carbon dioxide, because it evolved before there was much oxygen on Earth. Therefore a lot of oxygen was produced at the beginning, most of the oxygen we have today in fact, and then not very much thereafter.
Additionally, the Earth's oxygen levels stay stable due to the release of oxygen trapped in minerals. Over those hundreds of millions of years, they absorbed it. This absorption and release has kept levels stable for well beyond our existence.
At least that's what I got from the PBS video. If you don't agree, go argue with them, I'm no expert. I'm just forwarding what I learned.