Yeah, that threw me... it doesn't look that steep when he is driving up it. I guess that's why the engine sounds like it is kicking out a lot of power.
I can't tell which direction gravity is supposed to be going in this video. It looks like the snowmobile hunted the person down for revenge after the wreck.
See how damaged the snowmobie is at the end of the video? If he had just grabbed the thing halfway down the mountain it probably would have been fine and he could have gone back up.
It seems like every time a stunt like this ends up in narrowly escaping death or injury, the stuntist get very very angry. Or so has youtube led me to believe.