I still don't get why it failed, if back up drain can't handle the full flow from the return on it's own then you have quite a large issue. This is Herbie 101. I would hope you've fixed this so this won't happen again.
PS good luck with the folks, for the record it's easier to tell them these things over the phone when they happen. They can't do much from a different city so this would be the smarter play as appose to doing it all in person at once
