Like has been said about the chewing it sounds like this hurt him a lot, poor kid. But so good to hear the black is gone (that was scary) and that he's starting to put weight on it, and sooo cool that he has cagemates are in tune with and respectful of his needs. He might never have any further problems from it, just worth mentioning if he's at the vet is all so they can make a notation and if in future he has some trouble they'll be aware it might be related to that.
I love the pic in the little basket, but can we be greedy and have another picture of him too? And unless I missed it I didn't see his name?