It's so unfortunate when things like that happen and I'm sorry that you lost him! ):
As for the food, do you mind sharing what you fed him exactly? Was it a frozen/thaw or a prekill? If it was F/T, how did you thaw it? Also, considering that her was suffering from a previous injury, do you think he could have been experiencing some blood poisoning? That's always a possibility when dealing with wounds. A friend's corn snake go that way in the past, it was very unfortunate and unexpected especially since she too seemed to be recovering.