not to be a *****, but who would offer to shoot their own dog? what the heck is the matter with people? do i have chickens? yes. would i shoot my dog if they did this? no. thats what rescues are for. i am actively involved in animal rescue of all kinds, and i know that there are good homes out there for dogs that are prey driven. people just need to be more responsible with their dogs. i am very sorry this happened to your chicken, and i hope it can make it through. but i would also question a person willing to kill their own dog? or any dog for that matter.
A person that is very, very sorry would offer to do that so it never happens again. That person i would know was truly sorry for what happened and wanted to really make good with me. I think it was generous for him to offer that up, but I also think you were a very kind person to turn that down.
I'd cull the chicken.