If the flight is unfortunately cancelled it would likely be from around when they start the new services from Perth one would think, and if that's the case then the last A380 service won't even be able to be booked yet. One would think they would try to manage things so that minimal services need to be cancelled.The thought though that the QF MEL-DXB-LHR is under threat would actually make me reluctant to book one anyway now, for fear that your flight will be summarily cancelled and you'll find yourself in a middle seat on a MEL-PER-LHR, or worse EK on the same route instead. No thanks!
If my flights for 2017 are cancelled I'll probably ask QANTAS to move me onto a flight via SYD on QF metal if there's no other A380 route on QF metal.