I feed live, but I only feed one snake at a time so that I can be there every second until the animal is completely dead and they start swallowing for just this reason. I've had to intervene a few times over the years. Occasionally if I drop a rat in and the snake doesn't go for it right away, but I notice the rat sniffing around and touching the snake, I recognize that they are hungry and rather than risk any damage, I take the rat out and put it in my temporary rat cage for a couple days with plenty of food and water. The next time I drop them in, they usually aren't so interested in jumping on the snake and the snake in turn is more interested in them because the snake is no longer being made uncomfortable by it jumping all over them.
I'm so sorry this happened to your snakey.A very good lesson for everyone who feeds live though. I wish him a speedy and full recovery.