Just wanted to share outcomes.
1. Rang Cathay for my ticket, offered 2 nights accomodation or reroute via Mel or Syd. As expected would not touch other QFF ticket. They suggested to sort husbands ticket with QF and the they would then replicate what QF offered if we wanted reroute.
2. Qantas were terrible for my husbands QFF ticket Twice told they cannot communicate with Cathay and to suck up 2 day stopover. This was after being on hold for nearly an hour each time. Worringly they took e ticket number off the booking. Never got to the bottom of why they did that.
3. Finally on the 3rd go Qantas put an email request through to Cathay for reroute via Melbourne. So proposed itinerary is now ADL-MEL-HKG-JFK. ADL to MEL was on QF in J. Was told it could take a month to fianlise. Eticket from QF received 6 hours later.
4. Rang Cathay to get my flight sorted to replicate husbands itinerary. Took 15 mins but no dramas and still got ADL to MEL in J despite being told this might not happen.
So all in all good outcome, as we only leave Adelaide 3 hours earlier rather than 2 days. But honestly Qantas do test your patience and once again it's the poor suckers who are inexperienced in travel issues that lose out in these scenarios.