My late wife and I found a huge Alligator snapping turtle once that had been hit by a car. The shell was cracked open but the feet and head looked ok. Some blood was on the road. We used a tarp to help the big guy off the road and back to the water. I was later told that if a parasite did not set into the wound the shell would heal and he would be ok. They are resilient in general but even they have limits. Hope the guy you saved lives a long happy life after recovering.