> If the VS failed early on would the A/C have remained stable enough to transmit the ACARS msgs?
This could be reworded as "is relatively stable flight possible without a rudder and VS?" A B52 managed it once, but I suspect in general it would be a neat trick, especially in the middle of a storm at night.
That said, if the plane was stable enough to send messages and the VS decided to leave suddenly, I'd guess that it might remain stable enough to send messages for another few seconds, maybe longer. So if the VS had been the first thing to go, there is a reasonable chance that we would have seen a message about it. Instead we have a cabin descent speed warning.
Note that when the VS left it ripped up the back of the plane. The forward bolt support structure is very near the aft pressure bulkhead. So it might have peeled open the aft bulkhead. That could relate to the early reports that the bodies being found were from the back of the plane. Its possible the hole might not have been all that big, so it might have required some seconds to depressurize the plane.