My apologies for not giving more explanation of my quick answer. The hidden city is why I stated the remaining coupon had "no value". Just try to exchange it for a later flight! I don't think you'll be successful

Twice I was able to do this when I was flying through, with a connection in a non-hub city, but I misconnected and they let me use that second coupon at a later date. Once it was easy, no problem. The other time it was really difficult with various agents questioning the validity of the flight coupon. These situations were different from the scenario being asked about because the total cost of my tickets from A to B to C was GREATER than the cost of the flight from point A to B.