Given the (apparently, from press photos) relatively short debris field and the resulting state of the airframe, I'd guess it was pretty much a "fatal plunge" with very little directional control. I'd imagine that the ground speed was non-zero, but only just.
It's very sad event for the RV community. The RV-6 is a pretty robust airframe that has many examples flying for many years now, it's hard to believe it might be much else other than pilot incapacitation.