It's not actually all that deep, the man is stood in a trench he has dug up to his knees using spades, and using him as a 6ft tall scale the snow above the seating area is 8.5ft.
Rightly or wrongly I've always assumed that minus tools, cold and in the dark, and with the thermic clock against them, all the hikers could make was the simplest hole in the snow, not unlike the tent trench, and then effect a roof upon which snow from the spoil would be swept/pulled over.
So I would guestimate that the depth of hole they dug was 4ft, deep enough to cover 4 people sat on their behinds with their knees up to the level of their chests. Any deeper is just too much time and toil.
Through the subsequent 3 weeks, including the hurricane which would scour the mountain and blow snow as a drift towards the ravine, an extra 4.5ft has accumulated.
I don't think bodies would be dumped in a restaging scenario as this would fracture ribs and potentially be detected by the pathologist (accepting that the restagers may not be aware of this possibility), so they wouldn't be rolled or thrown into the ravine but placed there, their heads all to one side, if this theory was what happened.
Personally I have always believed the den was a triage made for 4 fading people, who died before its completion and were then respectfully placed in the ravine, or had been sheltering there during its construction. Then the surviving three, who wanted to make a safe haven for the 4 while they returned to the tent, spent time in the den, but by the time they tried to return to the tent hypothermia had taken its toll, they had descended below the recovery point and death was inevitable, all energy gone and all movement eventually physically impossible.
I don't think there was any snow collapse.