They used to give you the original mileahee if you asked but I believe there was a recent announcement that they would stop doing that. Maybe that's only for when the reroute is fewer miles rather than ineligible? I think it was an aeroplan announcement though I suppose it's up to AC whether to buy the points forthe route you didn't take.

On the plus side I hear the cx flight is a good choice. Pick up the 2.4k miles with oneworld and call it a win