If there are no localized observables in quantum gravity, does spacetime really exist, or might spacetime really be an illusion?
Andrew Strominger thinks spacetime is an illusion. It's all a Cosmic Hologram at the future boundary of spacetime at the end of time. It projects out the illusion we see around us.
The answer is divided more on the lines of "TOE vs. non-TOE" than "quantum gravity vs. non-quantum gravity". In string theory, the metric tensor is an approximation that arises as an effective description of the graviton field (see also this post on TRF). But in non-unification theories of quantum gravity, like LQG and its other discrete-spacetime cronies, spacetime is considered fundamental.