I don't get it!
Now that we found the vertical fin, we are speculating about this part as the primary cause of the accident or the first part that fell off. What if we found a door first? Would we argue then that it was a door that fell out first and destroyed the plane?
The reason why they found the fin first is because it is one of the very few parts nearly completly made of composite materials and thus floats (better than the rest). On most accidents over water they find the fin first (remember the Armavia A320 near Sochi, Russia, May 3, 06). Nearly always intact.
Those fins depart from the fuselage (for whatever reason) and "fly" like a feather earthwards. That's why they don't get destroyed on impact.
Dani