I reached the conclusion that Semyon's camera is the key to everything, the DPI cypher. The only theories which seem to work, tick the most boxes, are those which include why Semyon had a camera around his neck. It doesn't even require a subjective interpretation of the exposures, just why he had that camera around his neck during whatever unfolded.
It's the equivalent of your house being on fire and people are surprised you didn't grab your family photo's or valuables, just a telephone directory. The camera is useless for survival, but it may be useful for documenting evidence should you live or die, and you may hang on to it because of what you hope it already reveals.
This is why emergency theories like avalanche, slab slip, mudslides etc don't fit, unless, at a stretch, Semyon happened to be tinkering with his camera, the strap around his neck, when this happened and it then remains with him and it and the strap survives the disaster. But the greater likelihood is he made an active choice to take it, and above other tools more useful for survival.
The theories which include the camera are those which involve either an attack of some kind, or the fear of one. The camera provides incriminating evidence, where because it's minus a flashgun only the noise of the shutter may give the game away in the dark.
All these theories revolve around one initiating event where the consequences of the extreme environment then unfold. I don't believe that Murphy's Law delivered the worst hand through a single night, so that, for example, ball lightning chased them off the ridge after which they were hectored by third party humans and then died of the cold.
Military - accidental killing/mistaken identity at night, likely thermobaric grenades, fuel-air mixture expanding before igniting, delayed lung damage, embolisms, and soiling themselves, due to the way a vacuum bomb interacts with air/gas in the chest, blood/brain (microscopically) and intestines, head injuries from shrapnel or from being thrown by blastwave. Cover-up next day, resiting of tent, or if all hikers died at the tent on the ridge, the repositioning of the bodies at the cedar and den, to imply death was due to natural causes.
Deer hunter/Mansi/escapees - use hiker tracks to & from tent, force hikers out unprepared, occupy tent overnight, eat their food, vandalise tent in morning. Motive resentment, for Mansi/deerhunter, perhaps at 'noisy tourists' scaring off deer. Escapees, for food & shelter, perfect overnight cover from military search. Hikers die of the cold, possibly some finished off by Mansi to bury the truth as events will rebound on their community forever.
Group dispute & split - high stress on the ridge, knife fight in tent, knife held aloft by wrist pinned by another hiker, tent scored and then cut, tent useless. Cannot stay together overnight, or think survival chances better elsewhere, so Semyon's group leaves to dig a den (doesn't need wood cutting tools), Igor's group stays, then leaves to light fire as the cold descends (forgets tools & full clothing due to hypothermic effects). Fire fails, two die, then a Lord Of The Flies battle occurs, explaining knuckle injuries to the 3 most athletic, where the den 4 are murdered and their bodies put in the ravine. The victors occupy the den, and at first light try to return to the tent but die of exhaustion and exposure.
Fear- either after a direct confrontation, the hikers vulnerable and unarmed, or simply the fear of one drives them up the mountain unprepared, without sufficient fuel, and the cold does the rest in such an exposed position, and from exhaustion and the cold thereafter.