It's an internal matter and the contracting party is responsible for it. If I contract with you to send a catering staff and then in the morning I fire them all, I can't claim that it's not my fault. Even if they all quit, you still can't claim that.
You're not understanding the nature of contract law. When you sign a contract to provide a service, failure to do so is your responsibility. It doesn't matter if it was your fault or not. If they couldn't ensure the team they are legally responsible.
Furthermore in contracts for personal service it's accepted law that it's the special quality of the individual that matters. If a nightclub contracts with a company to ensure Deepika Padukone performs at New Years Night, they can't then send the owner's sister and say 'Sorry Deepika behaved unreasonably'. It just doesn't matter who's fault it was, they contracted to provide the service, they failed to do so, hence they are liable, that's all there is to it.