I’d like to know why they “decided” to fly across the biggest hill in the worst weather? Asking for trouble.
Can’t a Helicopter slow to a crawl and heavens forbid hover and turn around if they can’t see forward to avoid the hard stuff?
It's hardly ever that simple, unfortunately. Depending on weight and DA you may not even be able to hover out of ground effect sometimes, in which case forward airspeed needs to be maintained.
You also need to be able to see to hover (unless the machine is fitted with sophisticated equipment), so if you're trying to pick a way around low cloud in the hills and valleys, even at a slow crawl, it's a terrible situation to be in. Inadvertent IMC would be bad enough at low level over flat terrain in terms of maintaining control, but among the hills, even a max angle climb on instruments (assuming the helicopter was equipped and the pilot trained and ready for it) would be a lottery to miss the ground until you were above LSALT.
Even if you did happen to have a state of the art aircraft with autohover as per the modern EMS machines, it might be able to hold you in one spot, but I very much doubt it could get you safely out of a clagged in valley with high terrain all around (although I stand to be corrected, haven't flown these types).