His autopsy declares that he was struck by a flat object. Could be he was struck by someone wielding "The Stove" after all it was found on the floor of the tent or in its box. After perusing through all possibilities it is possible, Rustem the biggest and fittest of the group after pushing everyone aside trying to get out of the tent got what he deserved. The other side of his head maybe injured the previous day while skiing down the river and crashing through ice.
So many scenarios.
This field of Korumniki was a lot nearer than that shown on some maps and is another proposal for his injuries. You could walk as slow as you like through this horrific stuff and still slip and these guys were doing this at night or were they, whats the light like in the Nothern Urals at that time of year sorry but I have no idea working it out I would imagine dark at 6pm maybe.
Maybe thers another scenario that they Rustem, Igor and Zina were not returning from the cedar, but from near enough from where they were found. ie They set off but found the going too hard ,maybe the 3 of them injured so return to the tent for medical supplies.