I suspect this will be covered by Section 2, 1(c), where Aus Post will pay:
This section needs to be read in conjunction with all the other inclusions and exclusions... so for example Aus Post would work with you to determine the appropriate method of your return. If You had booked Qantas First class for $10,000, but they could find you a ticket on Emirates for $6,000, you would likely be limited to the Emirates flight. Or indeed if you could change your award booking to fly home for 'free' at a convenient time they would ask you to take that option.
In the event your FF ticket couldn't be changed, you lose your points, and they paid to fly you home in First class, I would suspect you couldn't claim twice under the policy. You wouldn't for example be flown home and get paid out for any missing frequent flyer points.
Any other issues where you might need to rearrange your travel such as weather, ATC (etc) would be down to the airline (under standard IRROPS recovery).
Will be interesting to hear what they say back to you.