If I recall correctly, once you reach the planned destination, the guidance finishes, the destination disappears but is held in the history. If the planned destination doesn't agree with where the destination actually is (quite often the case), then it will nag you to complete the journey upon restart. I've never seen a way to save a specific route (with or without way-points) on either the MZD or TomTom based systems, you can only save destinations.
Alan