I saw some rules like 30 years ago on survivor chances based on their behavior, I have trouble finding them but roughly it was:
Half of those who go unconscious but then wake up within an hour will survive
75% of those who vomit but stop within an hour will live, but 25% of those who cannot stop vomiting will live.
It went on into burn patients as well - it was data from the nuclear blasts in WW2. I remember it because years later when I did some medicine I realized the first one was brain injury and the second was intestinal radiation injury. If your intestines were sterilized you won’t be here much longer.
I think intestineal issues are the first symptom of your DNA being so fucked you can't produce new cells. The cells in your guts needs constant replenishment and things go bad quick down there without new cells.