Once the snow sets up(within seconds), it's not gonna collapse on him. It's the snow that is above and covering his head that melts from breathing that creates a shell that won't let air permeate and this is what could possibly kill him. In this case, his helmet is at the surface and I don't believe that he would have suffocated. Lets face it, if he can scream for help, he can breathe.
Tailing pile or not, that area is no different than the mountainous areas we all ride and should have been treated as such. Here in Colorado we have had 2 fatalitiesthis year in slides that were less than 150', the one was only 30'. 30 feet, people!