In fact, the very last Virgin Atlantic flight to touch down at SYD was VS200 on May 4 at 07.30am, which departed May 5 at 3.45pm as VS201. Virgin has cited increasing costs and a challenging economic environment for removing the Hong Kong to Sydney leg from the London-originating flight.
This leaves British Airways as the only European carrier to fly to Australia on its own metal (i.e. a British Airways plane rather than a codeshare with another airline). While speculation on how long the BA flight will continue is rampant, the British flag carrier seems committed to the route for the moment.
British Airways flies to Sydney through Singapore, with flight BA15 leaving at 9.35pm from London Heathrow, arriving at 05.05am in Sydney two days later. On the return, BA16 leaves Sydney at 3.30pm, arriving at 05.30am in London the next day.
Alternatively, you can still fly Virgin Atlantic to Hong Kong and connect there to the number of carriers with whom they codeshare for the remaining leg to Sydney.