I had a chicken with a huge ripped open wound down her side (and several smaller rips). We suspected a hawk attack. It was all the way through the skin, several inches long, and spread open wide. Not good.
In our case, we just packed the wound with Neosporin (without the pain relief) ointment. We did this for days and then weeks, keeping her inside the whole time. We thought if she wanted to live, then we were going to try.
It didn't seem like it would ever heal, but then one day, it started to close a bit. Then a little bit more the next day. It took a couple of months, but the wound finally closed. We couldn't even tell where it was after her feathers grew back in.
I know that ripped tendons and such are more severe, but I just want to give you some hope that these critters have strong wills to live.