Qantas has stopped all international flights as of last week (after reducing capacity previously). Air NZ is down to a few services out of LAX per week, only only a few connecting services to AU per week. So realistically as was said above, UA is the only realistic scheduled option for getting from the US to Australia.

As was mentioned above, both Qantas and Virgin (in conjunction with the Australian Government) are in the process of scheduling some "rescue" flights for Australian citizens coming from LAX, HKG, LHR and AKL, but it'll still be interesting to see how they choose to handle higher-risk passengers like those coming off cruise ships.