According to the local news, the female passenger in the crash aircraft was the wife of the pilot of the other aircraft and had changed aircraft at William Creek on a whim.
With todays navigation equipment, even in a RAAus aircraft, once you are in the cruise you know to the minute when you will arrive at your destination. If that is after last light the correct decision is clear. Hopefully the surviving pilot will shed some light on what happened so we can all learn from it.