Yep, it was a dick move that he stole this guy's article. That's basically the point. You can dial back your emotional involvement in defending him. Cheers.
DMCA is required as a first step to the lawsuit. IH agreed he was in the wrong legally and removed the video. If they sued him moving forward, it would have to be for something other than copyright infringement (plagiarism or conversion, for example), which is harder.
Nope. If the original video went up, it would be safe to assume otherwise. The new video is proof he did not acquire rights to resolve the DMCA.