A brief response as this is getting off the thread.
Tickets were booked in person at a QANTAS Office using a Senior Travel Consultant.
No changes were made to itinerary.
QANTAS made no attempt to contact us (some of our Hotel bookings were on the SABRE system), or warn us when checking in on tehe outward leg.
After some correspondence the final letter from QANTAS stated
"Regrettably, from our investigation, it is apparent that your return flight was inadvertently cancelled in this office, prior to your departure."
Hope you have a better experience next time.
Luckily the extensive use of the internet nowadays means that passengers can usually pick up these sort of problems.
So what QF are saying is that it was finger twubble by their travel consultant who accidentally cancelled the return flight in your booking.
Just a couple of points re QF not contacting you:
As your flight was accidentally cancelled by the consultant, he/she would have no reason to contact you if they hadn't realised what they'd done. I'm sure if they'd picked up the fact they'd cancelled your flight by mistake they would have either immediately reinstated it or taken other steps to ensure you got the seats back.
When you checked at the airport checkin staff only see your flight bookings for that day & oncarriage on other flights that day or in some cases the day after. If you for example flew outbound SYD/LAX 20 Jun then returned 06 Jul, the checkin agent would not see your return details on the checkin screen (Altea) so would not pick up you were meant to have a return flight.
If somebody was to look up your booking in the (Amadeus) reservations system only then would they see all your other flights in the booking. Checkin would rarely have any reason to look up your booking in the reservations system.
I'm assuming you didn't find out your booking was cancelled until you arrived at the airport?
What did QF do to get you home? Did you get any form of compensation for the inconvenience?
It's always a good idea to call the airline 24-48 hours before just to check everything is okay re flight times, special meals or assistance required & special meals if any. That way any problems can be dealt with then so it's all smooth sailing when you get to the airport.