The standard for this is actually a rather healthy 100,000 Avios or £750, certainly in paid F. Not sure if there is a difference if the ticket is a reward ticket. I took the Avios the last time it happened to me. It was on a daytime flight to MIA, so not the end of the world. I would have been thoroughly miffed had it been a night flight though.

The CSD/CSM should actually have been pro-active on board and filled in the compensation claim for your Dad. Did anyone approach him?