Starting from the basics. This is a slash, no doubt. This is also pretty much a tomahawk chop to Mark Stone's wrists as well. The rulebook states pretty clearly that if a slash injures a player, it's an automatic 5 minute major and game misconduct. So the rule was interpreted correctly. Whether the rule is a bad one or not doesn't even really matter, since when a player skates off the ice as fast as Stone did, one would rightly assume he's injured. 90% of slashing minors in the NHL look fairly benign, with the worst outcome often times being a stick broken in two. It's also impossible to know whether Subban intended to injure Mark Stone, so that too is moot.
Mark Stone was also not faking being injured. At all. We know from past experiences that hockey players a tough S.O.B's. Gregory Campbell is often lauded for the heroism of playing through a broken leg after he blocked a shot to finish his shift. Sure, there is now a diving hit list but in the playoffs, players will play through ridiculous injury even more than usual. One of the most fascinating stories when a team is eliminated is listening to the GM rattle off the injuries players were carrying and played through. It would take Mark Stone's wrists being held by a single strand of cartilage to keep him out of further action if he can conceivably play, even if he's not near 100%.
Yes, the Sens want an investigation (a "forensic investigation" if you will) into the play, but Subban isn't going to be suspended even though Stone is now not 100%. The league not only hates suspending players during the playoffs, this situation doesn't even warrant a suspension. One of the biggest issues with the DoPS is suspending not only to the injury but the player injured (see here for evidence), so keeping their finger off the trigger for once is a welcome change. A less than 100% Mark Stone is obviously detrimental to the Senators, but Montreal lost their best skater and promptly conceded 2 PP goals during the major (they did get a shorty, but that's besides the point). As much as one would say the Sens will have a whale of a time beating the Habs without Mark Stone, the reverse for Montreal and P.K Subban is also true.
As the brilliant Sean McIndoe (aka Down Goes Brown) points out, the fact that #slashgate happened in a Sens/Habs series is about the worst series this could happen in because of the many closets filled with tinfoil hats in both cities. Both sides are equally guilty of being equally ridiculous and over the top with their views. But after cutting through all of the rhetoric, angry tweets, and NCIS Montreal jokes, the simple fact is the NHL did everything exactly right.
When the NHL gets decisions like this one wrong, they are absolutely hammered for it. When they get the decision right, they should be praised in equal measure.
Time to warm up the praise chorus.