my take on what happened.
they cleared Italian airspace at about 10k feet, and started across the Adriatic towards the Balkans.
Their track becomes very erratic soon after, indicative of the very turbulent air in a storm cell. The transponder readings (plotted and released by Zagreb radar post event) indicate that they were in a heavy descent ( circa 50mph) - basically free-fall.
They impacted the sea soon after. I think they were hit by lightening and it damaged the balloon, which then fell apart on the descent. I hope they did not know much of the descent, pointed to by the fact they did not use their parachutes.
