This might sound a little contenscious, but if your leg was bitten off wouldn't you go to the doctor?

a)your turtle is in pain
b)your turtle would definately benefit from assistence to deal with this major trauma.
c)your turtle is at a serious risk for infection.

Without veterinary help, your turtle will suffer, and the odds of living vs dying would be I'd say 50 : 50. Raise the odds, make your turtle comfortable, and take him to your herp vet asap.

www.arav.com is a good place to find one if you havn't yet.

Ian