WOW, that's some bad stuff going on. If you were to take it in, if you were to find it again, do you have the space to keep it. I would imagine it would take quite a long time to heal him up and I'm not sure if he would then be able to be released back to the wild. On the other hand, will he live much longer in that condition? I guess if you found him again, that would be a sign you need to intervene.
Yeah i agree with Wellington, in the time it would take to heal, it would get used to tank life and being fed and then it would probably die in the wild. As sad as it is, i think the best thing to do is let nature take its course, you cant save them all...