Was a crosscheck to the face appropriate? No. Absolutely not. Given the complete lack of priors but also given the Parros Leafs tax, I would say he gets 4 games.
I would also expect a scrum or a facewash or a light shove as a more appropriate response. Imagine it's a football game and your team is leading, 10 seconds left, you have possession and the other team has no timeouts left. Do you kneel out the clock, or do you fake knee and then uncork a TD pass? What Grieg did was tantamount to the latter and that would at least draw a lot of chirping or shoves in any sport. It's just a basic "don't be a sore winner, because you never know when your team is gonna be on the other side of it" thing. It's not a hockey thing, it's in every sport.
Again, just to clarify, Rielly's response was way over the line and well beyond inappropriate. But if roles were reversed and Gregor or Kampf took an empty net clapper from in close, I would definitely expect them to catch heat for it.