Flying Durama is spot on. The LHR trips out of Sydney are only twice a week and 50/50 SYD and LHR crew. This makes the LHR base more efficient and certainly doesn't spell the end of the LHR base. OZ crew may be going all the way through to LHR, but on the flip side LHR crew are also coming all the way to OZ.
It's a positive thing for both bases.
It also may only be temporary, as it has been in the past.