Re the 139 auto approach
The 139 does have a 4 axis AFCS and can fly a very accurate approach to the hove and even do a go around when initiated. However it does need to be set up correctly including defined parameters and location etc. In this case, from what I can surmise, I think that the accident has happened in the early stages of flight and that the approach mode will not have been set up. Of course, it only works well when everything is working correctly.
Regarding the possibility of some sort of power loss, the 139 has excellent OEI performance but it does depend upon what is around you in the form of obstructions.
There are a number of possibilities as to the cause and the AIB will in due course come up with an answer. Speculation, "eye witnesses" and armchair "experts (spotters)" do very little to help the situation apart from spread bad rumour.
In my opinion JV is the radio equivalent of gutter press, he will always take a contrary argument and interview so called "experts" to get a bit of a sensationalist view on a subject. I stopped listening to him a long time ago as he never seemed to give an unbiased outlook on a subject.
God speed to the four who sadly passed away in this tragedy. My thoughts are with their families.