According to rule 70.4 in the National Hockey League's rule book, at a stoppage of play, if a player leaves the penalty box to engage in an altercation, that player is subject to a game misconduct, as well as a ten-game suspension.
Some are saying because the game is over, Pietrangelo is allowed to leave the box and join his teammates, which is absolutely correct, but when saying that, you're entering a bit of a grey area in terms of if the end of the game (final whistle) is a stoppage in play or not. And that is causing confusion among many hockey fans on Twitter.
We'll have to wait and see what the NHL's Department of Player Safety decides to do in this situation, but it appears unlikely that the Golden Knights will be without Alex Pietrangelo for Game 5 on Tuesday night.