As another poster mentioned, yotes can be exceptionally tough animals. I have been amazed more than once in regards to the amount of damage that they can absorb and still run off.
If all I had was a 9mm, I would use it, but (my personal opinion) I strive to give the animal a quick clean kill if possible, and therefore would skip it in preference to more traditional choices, like the .223, 6mm, etc. Under 50 yards, a shotgun, properly choked, with the right load is pretty stellar too. That said, the majority of the coyotes I have shot have been far beyond 50 yards.
.223 Tikka with handloads using a 52 grain SMK.