It is my understanding that QF only have A380 "standby" crew in Sydney.
Not true. At any given point in time there will be several cabin crew on reserve (often for a period of a month or two at a time) from both they SYD and MEL QCCA bases. Part of the pattern/rostering. In fact, sometimes MEL based crew on reserve will pax up to SYD to operate where SYD reserves can't cover.