But... all of your scenarios you gave can also happen with a 30cal... a cartridge isnt going to control animals reflex once its shot.I hope your billies don't do a death dive off a cliff and you are patient enough to wait for a shot to shoot him when he's not surrounded by cliffs. If he breaks or loses a horn and ends up with a red coat while tumbling down the mountain you may wish you used a 30 cal. What happens if the only shot you are presented with has a giant cliff below? Are you going to shoot?
Mature billies are built like miniature buffalo. They have extremely thick, dense bones, thick hide, thick hair, etc. I've been on several goat hunts where hunters wished they used a 30 cal.
Even the claiming of 'anchoring' an animal doesnt guarantee it to not fall.