Being able to observe something is quite different from being able to exist. Existence does not require it to necessary be observed. Such as dinosaurs, humans haven’t observed them but they did exist. Observation provides evidence of existence although, regardless of that existence is still possible.

I would say in the upcoming future physicist will definitely resolve for quantum gravity. For the time being I would say it is not a problem as they both explain the fundamental frameworks of the universe. But a combination of b0th will definitely lead to greater discoveries.