By the time you enter an orbit around the Moon (actually once you start a capture burn), you will need fuel to return. The free return is only a contingency for something going wrong on the first part of the mission. Also I am a bit foggy on whether a safe reentry is possible from a free return trajectory without any mid course correction burn on the way back. (Possibly that can be done with RCS only, though, which you need to put the spacecraft in the right attitude to survive reentry anyway)