Oh no Aaron, not the pup that was attacked by the dogs?
I've had to put down a few animals. My latest was in 2006 and she was such a good dog and a rescue. I thought I had more years with her, as the vet she was 4-7 when I got her in 2003. She developed what every vet thought was arthritis in her elbow, and then within two months it had turned into a tumour the size of a golf ball and all the bone had been eaten away. I was faced with amputating her leg and hoping it hadn't spread (x-rays showed she had growths in her lungs already) or calling an end to it. She was so sweet, but a neurotic stressball of a dog due to previous abuse. I knew she wouldn't take well to losing a leg, and putting her through that when the cancer was already so aggressive.... It was one of the hardest decisions I have ever had to make in my life.
I kept her comfortable until the day came when she wouldn't even get out of bed, she was in so much pain despite the medication. That was it for me. What kind of life is that, lying in bed in pain, waiting for the end?
Anyway, give Cayman a huge hug for me. If he's still running and playing and enjoying his doggy life, I would say why interrupt him? But if he has no quality of life left, then the decision is up to you. Aw Aaron, I'm really sorry to hear about this.