I saw QF2 is also on time from LHR-SIN, so assuming that gets off the ground to SYD on time and there are no mechanical issues to attend to on arrival for either flight, it should be looking good even if they were to swap the aircraft to the inbound from SIN.
I really don't mind at this point; we're lucky to have snagged Classic Reward seats in J when they up-gauged from the 787 and I just don't want a cancellation as there is no service on Friday this week and we have a connecting flight to Namibia on Saturday.

But hey -- if we can get off on time, even better!