Why did Igor die?

[GlennM]

I see your point. On the one hand. If the Yuris had succumbed to their injuries, I would think that the remaining 7 would all make for the tent as soon as weather permitted. On the other hand, if the Yuris and the R4 had all met with disaster, then IRZ would be the ones left to fend for themselves.

It does not seem likely that if everyone was alive and well in the forest, that only IRZ would set out for the tent. "Where we go one, we go all"

There would be no good reason for the R4 to stay holed up in the ravine and IRZ not to do the same because the same inclement weather affects all.

I believe that IRZ going back to the tent was a final and futile push for survival. They certainly stayed out in the elements too long, but they did not strip the R4 for clothing. I suspect it was impossible to do so.

IRZ must have felt lonely and defeated.

[Ziljoe]

you dig a shelter to prevent hypothermia; you don't dig one when you are already actively dying from it. By the time Igor was on that open slope, he was in the advanced stages of cold fatigue. Hypothermia destroys motor functions and executive planning long before the heart stops. He didn't build a shelter because his body was physically shutting down while he was attempting a desperate counter-march back to the tent to retrieve the gear he, or perhaps his friends needed to survive.

The snow on the slope was to all intent firn hard snow and a mixture of deep and shallow. IRZ were covered later by snow .

You build a snow hole in a suitable place to stay warm as you can and the ravine seems to be the chosen place . Igor most likely died trying to fight the cold , even if IRZ had survived a number of hours on the den flooring and it was a complete snow cave , the task to regain the tent remains but now with depleted reserves and severely compromised extremities.

It doesn't matter if it was murderers , a ball of light or moose chasing them about on the slope , neither if they were going up or down , the exposure killed them.