It very much depends on how far you are below MSA; a few feet, or even a few hundred wouldn't cause a problem, although it's surely better to stop your descent at MSA unless you are visual and are likely to remain so.
In the case in question, the helicopter was descended - perhaps visually - to 20'AGL. How do you then propose to climb safely to MSA in IMC? Entering IMC on departure from an un-surveyed site is fraught with danger (electricity pylons, telegraph poles, trees, etc). To maintain stability in the climb you need sufficient airspeed. This is why we have IMC envelopes. Even a climb at Vy at the highest ROC achievable is going to require a fair amount of distance.
I've checked my logbook, and this is an aircraft that I haven't flown, so I don't know what equipment it had, but a nightsun would have been nice. The landing lights on all the twin-squirrels that I've flown have been woefully inadequate for night departures from unfamiliar sites.