I don't know if Tony would have killed Ralphie purely due to the Tracee scenario. I think without doubt Tony was disgusted by the act and wouldn't have cared too much if Ralph were to pass naturally...
I genuinely think it was Tony's love for animals (and in particular Pie-o-my) and Tony's manic depressive rage that killed Ralphie.
It was clear Tony disliked Ralphie but I think if almost anyone had killed Pie-o-my (hurt an animal for money) for insurance money and also caught Tony in a manic depressive/rage state/mood, they more than likely would have faced the same fate. How many times did we see Georgie the barkeep copp it for little annoyances?
Tony's bad moods = danger for anyone in the wrong place at the wrong time.