Sick amphibians that won't eat are invariably doomed. Assuming the frog can heal from its injuries (which I doubt, actually, despite your vet's stitching), force feeding it may be the only way to get it to eat for the time being. Unfortunately, attempting to do so would be even more stressful and may not be productive in this frog's case. If this is a native frog, I would suggest keeping it somewhere nice and cool with plenty of cover and no possibility of predators or pets in the area that could stress the frog. Cold conditions have been shown to aid amphibian healing from injuries, and the cold weather will slow the metabolism, going somewhere towards mitigating the lack of appetite. Give it 7-10 days in these conditions and then check it to see how it's doing. I would avoid checking it before those 7-10 days elapse, as doing so will likely just stress the frog.