I was just confused with the word choice I suppose. Not all snakes are meant to live. Sometimes there's just something wrong internally. The best we can do as sellers is make sure they're eating, crapping and acting the way healthy snakes should. Sounds like you covered your bases in these regards.
I personally wouldn't feel responsible for covering any biopsies after the necropsy showed all clear. If a customer assist fed against my recommendations after such a short time, I'd be more inclined to believe they killed the snake with "kindness" than anything else.