You got a syringe with a cure inside it...you knew what to do with it. You wanted your old friend back. So you went to do just that. You made it back and went to that exact forest where you last saw him...Doggy. Still holding that same axe. You injected it into him and he slowly woken up. It worked...it actually worked. He was cured.

Doggy: "Huh? What happened? I last remember a horse and Willow forcing me to drink a green bottle. Then nothing. Huh? You okay there buddy? What's wrong. HUH!?"

You caught him off guard with a hug.