Hello Parsifal
I doubt that anybody knowns the number of those died in hypothermia and exposure.
And I really doubt that hypothermia and exposure were great killers in the Karelian Isthmus, were heaviest casualties happened in absolute numbers. Without doubt some unrecovered wounded died in exposure/hypothermia but it is difficult to say how many of them would have died anyway. And few late recovered wounded were probably saved by cold, because human bled less in cold, that phenomenon saved a few Finns also.
Between Lake Ladoga and Barents Sea. Encircled Soviet troops lived in covered dugouts. And anyway encircled troops without adequate resupply were stormed, surrendered, run out of ammo or run out of food/water sooner or later. That is a hard truth of siege warfare and had been for thousands of years. Cold only accelerate the food problem because of human needs more energy in cold weather. Almost all Soviet citizens knew what harsh winter means so they did not have many of the problems Germans had during winter 41/42. Undoubtedly there were cases of hypothermia and exposure in encirclements but I doubt that in significant numbers. After all the greatest losses were suffered by 54. Mountain Div which was the best equipped div for winter of the encircled divs and whose men were used to the climate. So IMHO the losses were decided more by the tactical situation than climate. IMHO maybe greatest number of hypothermia and exposure happened during the break outs. If one got lost in the forest situation was rather desperate. On the other hand it was more difficult to lost contact with your comrades because the route they had used was rather easy to find because of snow. And it was easy to catch them because going was much harder at the front of the column than at the rear of it.
Juha