BB: Your hypothesis:
1. They continued VFR into IMC which sadly led them to the Mull.
If 1. above is correct, are they guilty of the 'gross negligence' charge?
They may be. They may not. That would depend entirely on the precise circumstances.
What's your opinion of what was occurring in the cockpit of ZD576 at the time in question?
Of course we have to deal in 'matters of opinion', as we cannot deal in 'matters of fact'.