If the flights are still flying then I guess you would have to pay the change fee. If they cancel them I guess you wouldn't.

Any OneWorld airline can reroute/reissue the ticket in principle, although it is easier to persuade a carrier who has at least one long-haul segment remaining on the ticket.

Note also that BA will charge GBP25 in addition to the US$125 change fee as their additional fine for actually asking them to provide any service in return for your thousands of dollars purchasing the ticket. (I fear that QF may also raise such a charge - CX and AA are the best placesa for reissue if you can use them.)