The decision by an IR(R)/IMC rated pilot to fly the route does not seem unreasonable.
TAF COR EGPU 041206Z 0412/0414 29009KT 9999 BKN015 TEMPO0412/0414 1200 DZ BR BKN002
Well, if I wanted to fly a helo off a nearby ship into Tiree that TAF might seem reasonable. But it doesn't seem so reasonable given where the flight was coming from and the dirty great mountains they had to negotiate. One would expect a route brief indicating somewhat better conditions to that along the way, and no doubt the experts will be looking at that as they try to figure this one out.