Funny enough, the oilers actually did score goals while Pronger wasn't on the ice, in fact, there were whole games he wasn't on the ice for a goal for and they still won . True story. Heck, he wasn't on the ice for the last 3 goals (out of 4 total) they scored to win game six.
Doesn't have to be Pisani, I just chose him because he happened to score the one goal for edmonton (which Pronger had nothing to do with btw since he was sitting on the bench at the time). So maybe Smyth scores goal 2 and Hemsky goal 3. It doesn't really matter. Point remains that winning that game wouldn't have changed Prongers performance.
And again, this isn't about legacy, it's about performance. Winning the cup changes one, but not the other. Perfomance is independent of the game results. You can be good and lose, terrible and win.