There is nothing wrong with full chain guides used in DH (well, by most riders not hunting milligrams in all the wrong places at least), him crashing also didn´t have anything to do with chain guide, stop chains from snapping, that´s all that is required from this not happening. And chains not snapping belongs in the same bracket as not flatting tires, it´s not going anywhere anytime soon. If anything, the chain guide did too good of a job to keep the snapped chain on the bike long enough for it to get sucked into rear wheel.