Oh poor Shadow!! Those black squirrels are kind of thugs, aren't they! At 8, Shadow really shouldn't have much to worry about as far as age related issues and anaesthesia go. Max had a dental earlier this year, at 10 and did fine (and many other greys have, as well). The pre-anaestheia bloodwork is very important, and as a senior Shadow should get a discount. If you are worried, there is a vet in Guelph who just does doggie dentals - Fraser Hale, very good. They just deal with one patient at a time, so all there attention is on your dog. And you can stay the whole time, be there when they put him under and as he wakes up. For a control freak such as myself, that is very important! If he hasn't had a dental, really seems like a good time to do it, given this injury as well.
Hugs to the big black boy!!!