My injured cygnet friend looks like one of the family at the moment. He's a bit smaller and fluffier than any of the other five cygnets, and his wings are less developed, but he's with the family full time now as far as I can tell, and he's keeping up with them. His right leg must be getting very strong.
You can see how he carries the damaged left leg laid across his tail, keeping it out of the water when he's moving. It must just create drag.
The leg is clearly damaged lower down, so that while he can move the leg as a whole, he can't use the lower joints. I assume this is because the fishing line had reduced blood flow to the lower leg for too long.
The adults show the uses to which you can put a very long neck.