A few years ago, I was forced to check my brand new Hartmann roll-aboard on a flight back from Belfast. When I got it back in LGA is had a nice area that had been rubbed right through the fabric. It looked like it was held to a grinding wheel but it was more likely a conveyor belt run amok. I brought it to Delta luggage service where they noted the damage and gave me instructions for sending it in for repair which I did. The repair center sent it to Hartmann who informed them that it was "unrepairable". The luggage repair folks then offered to patch it but since it was new I objected. After some back and forth, they replaced the bag with a new one. That gesture kept me completely loyal to Delta and helped make me a Delta evangelist. They easily made their money back 100X over.
The Hartmann is still in the box it came in and was replaced with a Briggs and Riley roll-aboard that is built like a tank and is guaranteed for life regardless of who or what damaged it. I've used it almost weekly for the past 3 years and it still looks close to new.
Somewhere within Delta is someone who might remember what customer service is all about and may be willing to try and fix the bag. I wouldn't bet on it but it's worth a shot. Good luck.