I wouldn’t say it’s impossible, but I have my doubts. They had no shovels or buckets with them, so they had to have used their hands to dig ten feet of snow out from the hole. I know other people have done that to survive, but I have a hard time believing it, because they were inadequately dressed, and they would already have walked a mile from their tent in freezing weather. Even if they attempted it, I would think they would have died of hypothermia long before they had the opportunity to make the flooring. But, I’m no expert, so I don’t know that for sure.
However, they would have not been able to dig a hole with no tools if it was hard, packed snow. It would have had to have been the light, fluffy kind. I guess they could have still suffocated, but I’m not sure the weight of the snow could have caused the injuries they sustained.
I have been looking into another theory that usually comes up with the snow den collapse hypothesis and that is that their bodies were carried down to the place they were found by the water when the spring thaw came. Even that has its problems, though, as a current that can move a human body should have also moved the tree clippings and clothes, yet the flooring was still intact.