QANTAS'S flagship Kanagroo Route to London wil be the most effected by any war. Other then Europe everywhere else Qantas flies is in the Pacific or Indian Oceans. During the last Gulf War they looked into flying to LHR with a SYD-HNL-LHR routing. They could also operate via LAX and continue flying to LHR as a BA flight, even if QA doesn't have the traffic rights from LAX to LHR. I think that Australia will benefit from being a "safe" destination.
The problems at United can also be a benefit to Qantas. If UA stop flying to Australia I do think a US airline will pick up the route but QA will have the advantage. NW is likely but weak, CO flew and a 777 is likely but from EWR or IAH via HNL not LAX, DAL is unlikely & AA is a ONEWORLD partner with QA and now that it flies LAX-NRT, LAX-SYD would seem more likely. With all the flights from LAX to Auusie QA has it is and will be the KING.