You have shared a very interesting & thought provoking concept-
I have always thought that Semyon (aka Sasha) was the odd man out and perhaps his presence is key to solving this mystery. I still say that this event has homicide written all over it.
IMHO - this was a cold calculated killing.
I only recently learned of this mystery, and it has obviously remained an enduring mystery because no single theory ticks every box. But I do recall the first thing I thought was this will be like The Ten Little Indians
, or rather 9 because one dropped out. And my initial gut instinct was what was this older man doing with a younger group cramping their style, and also wondered if the one who dropped out returned to kill them.
When you read of this tragedy it's presented as though all the hikers were a tightly-knit group who knew each other well, all shown posing for smiling photo's, and this works towards making the reader imagine an outside force, natural or man, could be the only explanation for destroying this bond.
But then you read the diaries, and discover things like these:
Lyuda's diary 25/1/59 - The mood after the movie greatly improved. Igor Dyatlov was unrecognizable. He tried to dance, and even started singing: "O Jackie Joe"
Zina's diary 28/1/59 - ...I mended the tent. We lay down to sleep. Igor was rude the whole evening, I just couldn't recognize him. I had to sleep on the wood near the stove.
'Unknown' diary 30/1/59 - Lyuda quickly got tired and sat down by the fire. Nick Thibault changed his clothes. He began to write a diary. The law is that until all the work is done, do not approach the fire. And so they had a long argument, of who will sew the tent. Finally K. Tibo gave up and took a needle. Lyuda remained seated. And we sewed the hole (and there were so many that there was enough work for all except two attendants and Lyuda. Guys are terribly outraged.
Again on 30/1/59 - ...Burned mittens and Yurkin's second quilted jacket. He cursed a lot.
And most portentous of all, earlier on 26th: Mood is bad and probably will be for two more days. Evil as hell.
So a bit of an atmosphere, bickerings, mood swings until someone is unrecognisable, refusals to do work, not really operating as a team.
As regards Semyon, who coincidentally dies on his 38th birthday, and appears to be the only one carrying a camera at his death, he was one of two fully-clothed, which is taken to mean he was outside, and his empty bladder means he must've been urinating. But equally he may have been fully-clothed inside the tent because the stove was off, it was unpacked.
What if the others were somehow made to remove their clothing in the unheated tent, to induce hypothermia. Possibly after an assault or two he cuts his way out because he couldn't get past the others and unbutton the flap, and since he won't be staying he doesn't care about the future use of the tent, and slashing it renders it uninhabitable overnight. However this theory is flawed because he would have taken their clothing to guarantee their deaths.
If this madman was then on the loose, possibly shouting threats, they wouldn't feel it worthwhile attempting to stitch the tent in the wind, dark and snow, it isn't a building they could barricade themselves in, and he'll probably arrive to damage it further, so they evacuate. You'd still anticipate they'd take basic clothing though, and the madman should still have the knife used to cut the tent with which to stab people, so I'm not buying into this entirely, just speculating through a whodunnit theory.
It's assumed they all 'calmly' walk down to the cedars together, from 9 sets of prints, but equally the killer among them could have followed their trail, adding his footprints, and one set is said to meander and return to the line.
At the cedars they would look for firewood, and this would allow individual attacks, until they weakened and the fire started to die down, and as a result hypothermia killed two of them there.
Interesting too that at autopsy Igor Dyatlov's bladder was fit-to-burst with a litre of urine, not something normally associated with hypothermia. I'd speculate he had a urinary/bladder problem, and if his bladder was overloaded then apart from sweating, his kidneys would struggle to continue excreting toxins out of his bloodstream and his blood pressure may rise, changing his behaviour. This doesn't automatically cast him as a killer, but it might explain his changing moods, as recorded.