Thanks for everyone for your thoughts. We did call Delta last night and got nowhere with seating. When we did a dummy VA booking, exit row seats showed as available for purchase, however, on DL, those seats don't show as available, and the agent we spoke to kept saying those particular seats were already booked - so I don't think she could see them. We will look at our options and decide exactly what we would like to happen before calling again.
When I look at the booking on the Air New Zealand site, it still shows up, so I'm guessing they won't consider a refund until the booking falls off and who knows when that will happen.