Delta has lots of airport pairs that operate once per day. There are several destinations to which Delta operates just once a day (JNB, Exuma) or even less than daily. This isn't a problem confined to LAX-SYD; it's not a new problem in any way. Delta has interline agreements with all carriers on the route: QF, AA, UA and VA. Ability to get rebooked on another carrier will probably involve SkyMiles status, fare paid, and reason for delay. Delta routinely reports the best completion rate among major U.S. carriers - OP will get where he's going. If a one-day delay is going to be 'catastrophic' he hasn't planned well.