We fly enroute with navaids out all the time. VOR U/S? No prob. Where does it say that that is acceptable?
Under 121 Flag OpSpecs, B034(e)(7), which states
An approved area navigation system fix may be substituted for a required en route ground facility when that facility is temporarily out of service, provided the approved navigation system has sufficient accuracy to navigate the aircraft to the degree of accuracy or navigation performance required for air traffic control over that portion of the flight.