A few months ago my wife and I bought round-trip tickets from Sydney to San Francisco on United and then from San Francisco to Copenhagen on SAS. We flew from Sydney to Copenhagen but now it looks like we won't be returning to either San Francisco or Sydney. Can we (or anyone else) receive any kind of benefit from these return tickets which will be unused or will they go to waste? There are also a couple of round-trip short regional flights on United within California which will be unused.