Disappointment doesn't quite describe how I feel towards the Sharks, but still I'm going to try hard and take an objective stance on the Simek injury.
Before that sequence, it had been a more physical game, so Simek had already absorbed some contact. The Smith hit might've jolted Simek a bit too, so he could have been fuzzy headed - enough that he wasn't aware enough to brace for the Marchessault hit. After that hit, he was woozy but continued play. And with the cross check, that might have been something he would normally brace against if his head was in the right place.
And to give some leeway, it may be that the refs and players didn't know how concussed Simek was because play continued on. This is kind of like knowing if a boxer/MMA fighter is still mentally in the fight. If not, there could be a serious injury because the fighter can't properly defend a strike. Unfortunately, that might be what happened to Simek. And tragically Marchessault and others did not realize it and played as if Simek wasn't vulnerable.
Trying to hold my tongue, I would say the response was unacceptable and three people for sure carry the blame: Boughner, Couture, Gabriel.
Maybe no one knew how woozy Simek was, so there's a pass for why there was no immediate response or a response in the ensuing shifts. However, any of those three SHOULD have tried to find out what happened during INT2. To check up on Simek's status and check the replay. Obviously, NHLers are still pros and many know each other, so the response should not have been to injure Marchessault. But, there should have been a "check yourself" response to Marchessault and/or his line.
Boughner could have used that as a culture-building moment: "Simek got injured while fighting alone. For the rest of the game, we fight together and everyone will finish checks on the Marchessault line." Or Couture could have spoken up, told Boughner to put his line against Marchessault ASAP, and he would personally finish checks, even if a bit late. Or Gabriel could have taken matters into his own hands and gone after Reaves (whether he wanted to dance or not). I'm not sure that Couture or Gabriel did anything at all in the 3rd.
But, a bonus star goes to Meier and Kane for giving the Marchessault line some attention in the 3rd. I hope not, but I get the feeling they went rogue. That wouldn't be good for locker room culture knowing that a co-worker got injured and leadership failed to do anything meaningful.
EDIT: And the entire front office should be cleared, including the computers with their data. Having a lightweight roster play a physical style against a heavyweight roster is insanity. That's how you end up with Simek injured and Vlasic/Sorensen slow. If they want a physical style, they should acquire big bodies.