I had almost the exact thing happen to a friend I was helping.
His system was under warranty when the drive failed but he needed to recover some data on the drive that failed wasn't backed up. Apple would not give the back failed drive. So he ended up having to buy another just so he could send the broken one to Drivesavers. I still don't know what that did to his AppleCare extended warranty, I'm sure it voided it.