It would depend on how it was exactly done and his luck in ticketing.

LAX-HKG(stop)-SYD-HKG(transit)-LHR is valid under the rules and I think most or all airlines recognize this. The problems come more from travel agents and ticket shops that misinterpret the rules.

LAX-HKG(transit)-SYD-HKG(transit)-LHR is a matter of luck. I don't personally believe the rules allow it and most airlines agree. But some miss it and do ticket it now and then as has been reported on the board.

The OP in a subsequent post said they were going "to have to leave Australia (SWP) for the last." It sounds like they mean go to Asia first and then to Australia. That routing would be the first I mentioned and would be valid to use CX the whole way.

Would end up something like TPA-MIA-JFK-HKG-SIN-HKG-SYD-DRW-CNS-BNE-AKL//MEL-
HKG-LHR-DXB-LHR-LAX-MIA-TPA with two more segments available in each of North America and Asia.

To lpeterman, even with your wife, if you don't have time to stay anywhere else in Asia, see if you can get her to do a turnaround to NRT to use those two Asia segments. Not only is it 10k more miles, assuming you're then plat or exec plat, but it's one of the nicest flights I have taken on the CX network. Although I haven't had the kaiseki meal on CX, people are very complimentary of it. But even without, it's about a day trip and an easy set of flights. Maybe she would be less resistant if you were able to stay a night or two in Tokyo.