First of all, as has been pointed out, the first instincts of the 9 would have been geared towards surviving their desperate situation.
Secondly, perhaps they had an experience that they did not understand or would not have been able to convey in a few scribbled words.
Thirdly. Any "free time" to write would have meant that any of them were at rest, so, either a. succumbing to severe and no doubt extremely painful traumatic injuries, or b. in at least the moderate to severe stages of hypothermia, which are characterized by severe incoordination and confusion (people who have been rescued from near-hypothermic-death usually report hallucinations and disconnection from reality).
But its all pure speculation that you mention.
Not 100%. I would postulate that it is more than a little likely that a group of trained wilderness explorers, faced with a situation in which all their lives are threatened, would concentrate most or all their fading energies on upping their chances of survival.
My second point is, as you say, purely speculative. But interesting nonetheless, I opine.
My third point is also quite likely to be true. Outside of shelter and with inadequate clothing, hypothermia would set in rather rapidly. By the time they reached the treeline, without doubt. I have beside me three textbooks of wilderness medicine which all define mild hypothermia as being characterized by mild confusion and irrational decision making. Semyon, Lyuda and Tibo all had injuries that very likely would have precluded writing.
And I challenge you----if you have access to cold temperatures----expose yourself to even -5C for 40 minutes (minimum time from tent to treeline), with no protective handgear at all, and see if you can write legibly afterwards. I went out today at -14C without gloves and, after a walk of 6 minutes, could barely use my smartphone. I'm sure I couldn't have written legibly.