Unless the hotel was actually "owned" by Marriott I don't see how Marriott had the reservation. Every hotel I've been at is "owned" by some local company. The reservation is taken by Marriott, but is taken on behaf of the hotel. If the owner of the hotel decided to change to Super 8 then it is the hotel itself that should be held to honoring the reservation as the reservation is with the hotel not the company he's getting a franchise agreement with.

IMO Marriott would gain major customer points by doing something for this customer no matter if they have to or not.