I have yet to see any avalanche signs vanish other than melting and I live in an avalanche area. The road I just drove on was closed 2 weeks ago for an avalanche and the signs of the avalanche are still clear, and it was a very small one off a rock wall that just blocked the highway.
I disagree they thought more would come down because 1. they knew the slope they were on, if the slab that fell was the cause, they knew the slope wasn't enough to cause any thing to worry about and
2. any experienced hiker/skier knows that you run sideways from an avalanche, not down hill.
3. they walked slowly down hill from an avalanche? that makes even less sense
I really think the word "avalanche" is the wrong word to describe what might be more reasonably called "downhill-snow-movement" theories. The word "avalanche" connotes movement of a LOT more snow than would be necessary to trigger the Dyatlov Pass Incident. If some downhill movement of snow was indeed the root cause of the DPI, we can infer that the volume of snow that moved was not all that large, considering that it did not uproot the tent, and only halfway collapsed it.
I have recently expressed my current view of
"avalanche" "downhill-snow-movement" theories
here. I do not think it's far-fetched to believe that, when the Dyatlov Nine cleared a level "platform" in the snow for their campsite, they destabilized the uphill snow, in a "column" as wide as their platform. Then, due to gravity, some of the destabilized snow would settle, downhill...onto the platform...into the campsite...and onto the tent.
And then, we reach what is, in my view, a really crucial component of any credible
"avalanche" "downhill-snow-movement" theory: after some snow fell onto the tent, the snow in the uphill "column" had stabilized (for the time being); but when the Dyatlovites attempted to clear away the snow on their tent,
MORE SNOW kept coming downhill, to REPLACE what they had cleared away.
So, at any given time, relatively little snow moved downhill. But, because an entire uphill column of snow had been destabilized, a lot of potential energy in that snow had been freed up. So, imagine the situation from the Dyatlovites' perspective: for every kilo of snow they clear away from their half-buried tent, another kilo slides down the hill to replace it. In such a scenario, it's understandable that they might abandon their campsite (especially if their digging tools kept getting buried under snow...although I'm not sure if that was actually the case).
(This all assumes, of course, that the Dyatlovites pitched their tent at the place where the official search found it. I have my doubts about that assumption.)