Yes, I have to say I got quite invested in this case after seeing this thread, and my admittedly amateur research into it makes me think that he might be the sort of man who gets off on leading confident women into situations where he 'strips' them of their power.
So, charming and lovely at first, but then feeling the need to cut them down - by sabotaging them, pushing them beyond their limits, getting angry at them and making them feel small and weak, before leaving them distraught and frightened and making him feel powerful.
If that's so, then I think in this case he pushed her too far (or perhaps her viral infection made her fail even faster than he expected) and he either left her there to die, not wanting to risk her telling authorities about the dangerous way he'd behaved that night, or she slipped and fell, and he was unable to pull her back up, and again, left her there to die.
It's all just idle speculation of course, but based on his inconsistencies around what happened that night, and how he claims to have left her versus how her body was found, it seems as though while I'd believe he didn't ascend the mountain intending to murder her, that is how he descended it. Having deliberately left her to die.
As I said above, I wouldn't be surprised if, in a year or so, this happens again.