It's really sad watching that video knowing how it's going to end. Whatever maneuver Ziggy was trying to pull off there looked improvised and unrehearsed. I'd imagine that once he got up to the apex he probably said to himself, "Oh sh*t. This is not good." His airspeed must have been very, very low and his lift/thrust was pointing in the exact wrong direction. He was, as has been pointed out, at the will of gravity at that point.
Obviously he would have had to roll out of that steep bank and then recover from the dive. He probably did have the cyclic all the way to the left stop but the ship just wasn't responding what with the combination of low airspeed, bank angle and power applied as we know Bolkows are prone to (not) do. And there wasn't enough altitude to dive for more speed.
A long, long time ago when I was a mere private pilot, I'm ashamed to say that I crashed a ship doing something similar: an ill-advised ag-turn which I had seen done but never had demonstrated to me. Had I started with 60 mph it probably would've worked out okay. But I only had about 45 on the clock. At the end of the field I pulled the cyclic back. The nose came up and the ship...just...sort of...stopped, hardly climbed at all. I pedal-turned around, pointed straight at the ground now and went, "Oh sh*t, this is not good." Luckily I managed to get it more or less level before Bell 47 parts and pieces started flying everywhere. Result: One Bell 47G-2 destroyed. Completely my fault. I've lived with it ever since.
Difference between me and the Bolkow pilot was that he knew what he was doing...or so he thought.