Hi Karen,
Couldn't have said it better.

Wish we could find his death. Nothing from the Church yet so I will ring them again.
It is possible that Maria had problems with the birth of the last child and went to Sydney to recover.
It is also possible way out where John was working that he died from an accident and his death was not recorded.
Wish we could get employment records or Post Office Directory information for the area at that time.
Would it be worth getting a transcription of Maria's death or even her certificate online as this is a bit cheaper?