Another uncomfortable fact of life: Aneurisms. Many folks have them within the brain and/or along primary blood vessels and have not ever learned of that fact, for many reasons, until one day, poof. Death occurs quickly and one drops exactly where they were at that moment. One can be standing in an Emergency Room of a modern hospital and there is not anything that can be done for them.
It's not necessarily instant. Any hematoma inside the skull is bad news but may take hours to disable or kill. Worse, the victim can feel fine and I'm not sure any field test can always uncover the disaster until too late. And there may not be any sign of an impact on the skin either
If someone reaches ER in time a hematoma can often (usually?) be treated. A couple of years ago a baseball pitcher took a line-drive to the head and was rushed to a hospital where they found an epidural hematoma - he survived because no time was wasted seeing if he got a headache before doing a CT scan. By contrast Natasha Richardson died because she felt fine after hitting her head and didn't go to ER right away; by the time she felt unwell it was too late (and ER far away).
It's not hard to imagine that Karen Sykes slipped and fell earlier in the hike and then hours later was incapacitated by a hematoma, unable to use any of her protective gear, and that hypothermia got her first.
GetThereItis generally refers to the perceived need to accomplish a goal (get there) that overcomes training or good sense that doing so would be dangerous and potentially life-threatening. An unfortunate common cause of aviation fatalities.
This was called "Go Fever" at NASA and was viewed as a key element in the events resulted in the Apollo 1 fire.