If this was a club-operated aircraft who signed them out - surely with the weather forecasts available and the route known it was a 'no go' from the start?
As MaxRed stated:
That is a no go in my book, and would suggest most peoples. It was not even predicted to improve.
If it was a privately operated flight, it's sad that no one questioned the viability of the flight and/or had a quiet word in their 'shell-likes' when they booked out. All good advice in hindsight I know.
There are many issues here it would appear - not least IMCr v IR, MSA, published procedures, freezing level, TAFs and actuals ... the list goes on.
It's one of those accidents which makes you feel that the system's failed them somewhere?