My thoughts go out to the co-pilot and the other fatality and injured. Just by looking at the aircraft reminds me of other twin otter crashes I have witnessed, it is still a very strong airframe though and people have survived remarkably well in accidents in this type.
The flap system, post crash with wing separation, will lose pressure/fluid and therefor the flaps will droop if not supported by something else. So you cannot draw conclusions just by looking at a couple of pictures ok.
Yes the flaps are a very important part of the Twin Otters capabilities and should be used according to the situation. Hard runways on wheels will not usually nesssistate the use of STOL config and you will gain enhanced crosswind authority if you use standard flaps 20 for landing and 10 for departure. But, having said this, there is still adequate control up to the cross wind limits using the STOL configuration. So it comes down to handling/technique and experience.
Lastly, operating next to coconut tree lined runways in heavy crosswinds isn't easy and sometimes down right tricky especially onto short wet runways.
My impression is they may have bounced on landing, got slow, attempted to go around and power came up differentially. Then a loss of airspeed may have led to wing stall and subsequent impact with ground.
I ain't no crash investigator but I can understand how these events can occur from personal experience and close observation. The Twin Otter is still marvelous but when I think back to my early days as a fresh FO on her I can remember how tricky it was to ease down during heavy crosswinds in wet runways.