The collapsed snow wall is a better idea IMO than an avalanche.
Because although it would depend on the amount of material and travel, I find it hard to conceive of 9 people being caught up in an avalanche and nobody has a broken limb or finger. They mainly have crush injuries to ribs and fractured skulls.
I looked up a study of avalanche injuries, and while fractured ribs appears to be one of the main traumas (while none had fractured skulls) broken limbs feature the highest, and spinal injuries are also common. Out of 105 cases studied 18 had broken limbs or dislocated shoulders. 16 had broken ribs.
I'm in the "They thought it was an avalanche" camp.
But in order for me to credibly sell that idea, the evening in question would have to involve a really
terrible snow and wind storm. I think the picture of the hikers digging out a place for their tent shows that weather conditions were already bad. That picture looks like there is a whiteout condition going on in the late afternoon or early evening.
So suppose sometime during the night -- probably just after midnight -- the weather gets so bad that wind gusts are threatening to blow the tent down. This could happen if extremely cold air flows up the west side of Kholat Syakhl and down on to the side Dyatlov's group is camping on. Kholat Syakhl is concave-shaped on the west side and maybe that helps funnel the wind to the tent.
The thought of the tent collapsing keeps the hikers awake. Perhaps a partial collapse of the tent results in Nikolay Thibeaux-Brignolle (Tibo) and Semyon Zolotaryov getting dressed and going outside the tent to investigate. Those two are found to be the best-dressed of the group and they are in theory outside when the "event" happens.
Igor Dyatlov creates several small eye-level slits in the right side of the tent to communicate with Tibo and Zolotaryov while they are outside inspecting and/or fixing the tent supports. These eye-level slits don't seriously compromise the environment inside the tent because they are on the side opposite the source of wind. Dyatlov has a flashlight in his hand which he periodically turns on and points through the tent slits, perhaps to monitor the progress of Tibo and Zolotaryov or to signal them from time to time. A decision may need to be made soon to relocate down the slope to a wooded area if the weather does not improve.
Then the event happens. Severe gusts of wind moving up the west side of Kholat Syakhl pick up large amounts of mountain snow, which then rain down on the east side of the mountain. In the crosshair is the Dyatlov group's tent. The snow falls down on and around the area of the hikers' shelter. In the severe weather conditions, the two hikers outside the tent and the seven inside cannot distinguish this from the beginning of an avalanche. Taking no chances, the seven hikers inside the tent cut their way out either because the entrance is thought to be blocked by snow or it is simply the quickest and easiest way out. Snow continues to fall onto the tent as the nine hikers -- most of them unprepared for this and not fully dressed -- quickly leave the area in fear and seek shelter in the treeline below. In the chaos and confusion, Dyatlov drops his flashlight, and it is later found on a pile of snow which fell on the tent. This snow appears to be windblown snow to the search party that later follows because, well, it is. But most of the windblown snow that fell vertically is later blown away before rescue searchers discover the tent.
One-third of the way down to the sheltered forest area, Rustem Slobodin falls and sustains a skull fracture and two head bruises. During this incident a flashlight is lost, and even though it is still on in the darkness, weather and snow combine to conceal it (Or, alternatively, perhaps it was placed in a visible location intentionally as a guide back). Slobodin continues on with the rest of the group to the treeline below.
Once there, the group starts a fire under a cedar tree. Everyone tries to collect branches to start a fire, with Yuri Doroshenko and Yuri Krivonischenko doing much of the tree-climbing. The fire is started but it is too late for Doroshenko and Krivonischenko and they eventually succumb to hypothermia.
Eventually the modest fire wanes and a decision is made to seek different shelter. The surviving seven have different ideas, however. Leader Dyatlov thinks the severe weather on Kholat Syakhl has subsided and the tent and supplies can be salvaged, while Zolotaryov thinks it is best to shelter nearby and get the supplies they have previously cached elsewhere during daylight when the weather is more favorable. So Dyatlov, Slobodin and Zinaida Kolmogarova try to return to the tent, while Zolotaryov, Tibo, Lyudmila Dubinina and Aleksander Kolevatov build a shelter "den" in a river ravine using branch materials collected earlier. They also take some clothing from the deceased Doroshenko and Krivonischenko.
On their way to the tent, Dyatlov, Slobodin and Kolmogarova succumb to hypothermia. Zolotaryov, Tibo, Dubinina and Kolevatov leave their ravine den but slip and fall a short time later back into the river ravine after unknowingly walking on a snow-covered ravine edge. All four sustain severe fall injuries and are covered by collapsing snow and snow that falls later in the coming weeks.