Go back to your terms and conditions of the ticket, most likely NWA will not budge in goodwill. However, most likely in the terms NWA would have had to offer your father a full refund if they hadn't offered the same class of service, regardless of reward ticket status. Sounds like your inexperienced agent at your point of departure made the decision for NWA that you were going to be rerouted in the same class of service. This happened to me once on Continental, and I wasn't going to let this one go, I took CO to small claims court and got my entire ticket price and miles back. The judge felt that CO was obligated under the ticket terms and conditions to provide me with the same class of service OR refund my ticket since I made it clear to the agent at the time of crisis that economy was not acceptable.

Fight this one! The MPLS Star & Tribune has a great column for travelers rights when in crisis, try to get the author and email him to see if NWA will respond more to the news if you don't want to go to small claims court.