Yes they have simply rusted away by the looks of it. If you want to keep motoring remove them or the one. The rear brakes don’t get much heat to them they just serve as a shield, the fronts scoop a little air for cooling.
My NC fronts rusted more than the rears, check those too. I’ve changed the fronts on mine, hubs off I’m afraid same as the rear to remove properly and replace. The fronts were a pig on mine to remove, the hubs get welded on with years of rust..