Whether you can get a refund for the return segment or change it depends on the specific fare rules. The former is almost certainly a 'no' unless you bought a refundable fare, which I doubt you did. There is no punishment for skipping your return flight, but all remaining segments will disappear with it.

You may find that a one-way on Emirates from Australia to wherever you live will be very expensive (possibly half of a full-fare). Check this out before you decide to skip your final flight. You are probably better off paying a change fee on your existing ticket.