I have fairly reliable information confirming the pilot's body has been moved to Port Moresby.
The PNG AIC, web site advises a pre-lim report will be made available in 30 days, standard practice, more an acknowledgement that the accident took place.
Assuming the pilot was not incapacitated, the weather in the area was reported as being extremely bad and had been for some weeks. Strong S/E winds blowing up against the mountain etc. etc.
A highly experienced Ag-Pilot does not necessarily make a good PNG Pilot. Ag Ops take place in exceptional VFR conditions. I would suggest with nothing to support my claim but 99.9% no chance of such a robust airframe failing.
What I do know is that genuine PNG villagers are able to articulate themselves very well; if they say or suggest that the aircraft appeared to be making a controlled landing into the river, perhaps due weather, then that's the way the AIC will report it. We just need to wait and see what the AIC come up with …….