If this Piper was owned by Fay Keely and it's now sitting on the bottom of the English Channel, I wonder if the insurance will pay out if it was being operated illegally?
However I won't be at all surprised if it turns out that the aircraft had been hired and the pilot was volunteering -- flying for fun, as at any gliding club with a tug or at a jump club. Perfectly legal.
Flying into sev icing at night over water, however, was never going to end well. By all accounts the pilot didn't have the rating to fly IFR in Class A airways, safely above the weather. His other option would be to stay below the freezing level (about 3,000 ft that night); that would have been... Bold.