There are 2 primary flux paths in a permanent magnet brushless DC motor. One from the north face of a magnet to the stator through the coils/windings then into the south pole of the adjacent magnet. The other flux path would be from the backside of the magnets through the rotor metal they are attached to into the adjacent magnet. This second path does not contribute to the overall torque of the motor. Does it matter if the metal in this second path gets over saturated with flux? The material of the rotor would get to non linear magnetic operation... but would that affect the first flux path at all and the torque?