I've just seen it on +1 - quite extraordinary. Appropriate name, Dementyev, though Donohoe was fighting hard as well. I think the red mist descended on both of them, to be honest.
C4 were suggesting the Ukrainian would be relegated and the Australian given the gold, but the results are shown as final on the Rio 2016 site and Abraham Gebru's shown as the winner with Lauro Chaman second and Andrea Tarlao third, Donohoe 5th and I guess Dementyev DQ'd (and taken off on a stretcher into the bargain).
I've just tried to find the time stamp in the live stream to link it here, but I'm finding the live stream is freezing my browser so I've given up. It is tagged with a big yellow splotch on the live stream though as you say.
edit - they've also put up a clip of it at
http://paralympics.channel4.com/highlights/finish-line-crash-causes-contoversy-men-road-race/ but the clip doesn't really start early enough to see the initial blocking that led up to it.