That thread has many examples of skates going dangerously high.
Most are not intently to prevent the player with the puck from skating.
He held up and stuck his leg out. This wasn't in a intent to kill or cut his throat, the intent was to impede Adam due to having the puck. This was reckless, and it got worse when his right skate hits Adams skates. That's 100% a penalty, which is worthy of a suspension if there's a injury due to a clear penalty. The game didn't get to finish so there were no penalties handed out. Had it gone on without serious injury it would/should be a penalty.
Now what do you do when a clear penalty leads to a death?
He should 100% not be allowed to play hockey again. Not just for sake of punishment, but for his own well being of being able to move on in life. Something Adam doesn't get that choice because of his bad choice he should be accountable for.
At worst, he may get in a civil lawsuit. But he won't serve time because he wasn't looking to kill him, that's just the result of his reckless play. One that is pretty compelling from the video. Grainy/blurred and all plus his history of how he plays the game.
I don't feel for Petgrave other than it may end up costing him the rest of life dealing with it. But he did the act and should be reduced reliving it in civil court.
This should also be example A: Why reaching for plays that are not there are a bad choice because, generally it's the other person who suffers for your bad decision.