The documents suggest that this fracture to the skull, resulted in some clotting of blood (not their exact words). I.e., there was not the expected volume of blood loss, that would be associated with this massive head injury.
Thus, it would appear that JBR was already dead (perhaps seconds or a minute or two), or dying. Blood flow to the vascularized tissue in the head, had already begun to stop or stopped.
Would JBR have survived this injury if it were the only injury she had? I am not a brain surgeon, but from the looks of this fracture - I don't believe so. I think there would have been such massive swelling of the brain, that you would not have been able to keep the brain inside the skull. People have survived massive head injuries, if they are able to have emergency surgery to temporarily remove parts of the skull, in an effort to relieve swelling. There was an incredible amount of damage.
Editing to say: This devistating blow to the head, after JBR was already dead, suggests to many that JBR was effectively "killed twice". i.e. over kill. An important fact to consider, when developing a profile.