I'm sure that Notre Dame could have found any number of teams that would've been willing to cancel on someone else to play this game. It isn't like BYU was doing Notre Dame some huge favor, and we're playing this game just for them even though it is not in BYU's best interest.
For me, being on good terms is more about not being whiny. If BYU had said "no thanks - our schedule for the season is set and we don't want to mess with it at this point", I don't think that makes Notre Dame upset in any way. They just find someone else.
What I'm trying to say is - people in the program decided they wanted to play this game. This isn't just about what's good for Notre Dame - someone in the AD decided this was good for BYU too.