There is a cost involved to the contractor to hiring and training a new driver. And if it's a recurring problem I'm sure the contractor will have his contract pulled as they would be a liability to FedEx. Don't kid yourself and think you have immunity.
No immunity at all and not all turnover is bad turnover. And don't put so much stock in Nick's horror stories. Contracts are not terminated with that much regularity. Just think. They could pull a contract only to find the replacement is ten times worse. Turnover in contractors is more serious than driver turnover.