Yeah done that but not being fluent in Portuguese I bunged the bit under discussion into Google Translate and :
In fact, that report plasmava one of the worst cases to investigators : the probable scenario Madeleine is dead , and his body hidden in the vicinity of Praia da Luz.
So we don't have a direct translation of "plasmava" and most plausible becomes probable which is pretty the same in intent if not grammatically.
So back to original question why do you think he said "the most plausible" or "probable" ?
Or as I might it "yeah but stands a chance". Now when I say that I mean just that. My other would be "yeah well it's an odds on racin' cert".
So cutting to the chase when Sr Amaral said "most plausible" or "probable" do you not think he meant just that? rather than anything more definitive?.
Perhaps Montclair might help on the meaning of "plasmava" in Portuguese. My understanding is that it means "gave substance to", "gave shape to" from the idea of moulding an object from a lump of clay or wood, for example.
FM was relying on the English translation, which is inaccurate. The original doesn't say that Harrison's conclusion led Amaral's team to believe that there was no doubt that she was definitely dead.
I don't understand why, after all this time, this was never corrected in the translation.
As to the most probable / plausible scenario issue...
Harrison had apparently presented statistics of the various relationships to a child, when a child had died in suspicious circumstances and had expertise in the most likely dumping places of least effort in the surrounding area.
I don't have a problem with that, as people close to a child (by relationship or by proximity) are often responsible.
But it was a ground-clearing exercise. No trace of her was found.