Gentlemen: Speculation is more interesting when it is consistent with the currently-known facts. The vertical stab was in the drink, roughly along the flight path and between JFK and the spots where the engines landed. The main part of the a/c landed on 133rd st; the two engines wound up at 128th and 129th streets, respectively.
This would seem to indicate a strong likelihood that the fin separated from the craft before the engines did.
Source for engine locations:
NY Daily News