In the event that you have to fail a contract (you got ganked) always inform a Senior pusher or the CEO. Also, so customers are left confused, send the customer a friendly letter explaining that you lost the contract. Most customers understand that these things happen on occasion. NEVER link the killmail though as we do not reveal our haulers.
We do not have a template for fail mails but use your own judgement and be friendly about it. If you need any assistance in writing a fail mail please ask a Senior or the CEO for help.