It seemed to energize the Bruins. Rome wasn't a big factor, and wasn't a make or break type of guy. Horton was definitely having a good playoffs and this was a blow to the Bruins. If anything, you take that 8 days a week if you are the Canucks. Horton out and Rome out. No contest. The winner is the Canucks here. Horton is clearly more important and vital. However, that wasn't the case. I think the Canucks get pounded that series anyway, but it seemed like Game 3 was that game that shifted and made you give notice that the Bruins were making this a series. Whether or not Horton getting hit made that difference or not I don't know. But things I remember in that series were Tim Thomas literally bodychecking Sedin with an open ice hit. He sort of did a poke check/body check at the same time. It was brilliant. Also Marchand just punching Sedin without a Canuck coming to his aid, and without Sedin putting up a fight or even trying to block it. There was just so much that made you realize the Bruins were overwhelmingly better physically and eventually over a 7 game span the results would show this.
Someone said Stevens on Lindros. Yeah maybe. It was Game 7, less than 10 minutes in and Lindros had only 2 minutes of ice time. The Flyers outshot the Devils 27-18. The game was won 2-1 on a goal with two minutes left by Elias, so the Flyers were definitely right in the game until the end. But I think Lindros knocked out of the game is a huge blow.
Robinson hitting Gary Doernofer in the 1976 finals in Game 3 (?) comes to mind since it was such a thunderous hit against what was supposed to be an intimidating team. I believe they had to stop the game and hammer the glass back in. Robinson certainly helped tame the Broad Street Bullies.
Kevin Stevens getting hit by Rich Pilon and knocked out of Game 7 in 1993 comes to mind too. Stevens faceplanted on the ice, the Pens did take it to overtime and outplayed the Isles as if they were Peewee kids but I think losing Stevens in that manner really affected the Pens that game.
Lastly, Valeri Kharlamov getting whacked by Ed Van Impe may have been the icing on the cake for the Soviets in their game against the Flyers in 1976. It led to the "We're going home" legendary moment. They were told to come back on the ice or else they didn't get paid, but I think that hit was an example that it was going to be a long night for the Soviets. And it was. The Flyers drained them. Outshot them 49-13 or something like that, and won 4-1.