It happened to our Foot dog a few years ago. His sack got cut open and a testicle slid out. This happened in the middle of a hunt. So James just cleaned the testicle off real good, put it back it the sack and then put a few staples in to hold it closed. Foot went out and bayed another hog about 15 minutes after all of this.
He healed up just fine and even fathered a litter of pups for us. I hope everything works out well for your dog.