there is NO suggestion nor should there be, as to how/when/why the vert stab came off. It is off and that is the only evidence we have before us.
With respect PJ2, I believe that some conclusions can be drawn from the failure of the VS / fuselage connection seen in the photographs.
A simple knowledge of mechanics tells us that a large sideways force was exerted on the VS
at some unknown instant, generating a bending moment sufficient to fail either the bolts or the lugs (or a combination of both) holding it to the fuselage. It is not clear from the photographs whether the lugs or the bolts failed.
That sideways force could have happened towards the beginning of the sequence (as in the AA A300 accident), or at the point the VS hit the water, or any point in between. Time will tell.
The VS is a vertical cantilever. The VS failed at the point of greatest bending moment, occurring at the base of the cantilever (point of attachment to the fuselage).
From a simple analysis of the geometry of the complete VS / fuselage connection, there is no other plausible failure mechanism that explains the failure shown in the photograph.
Added - ChrisVJ, you posted while I was writing, I am very much in agreement with your thinking, particularly your last paragraph!
FBW