Good question, because other than Boyle who else was missing on defense? Niedermayer is hurt. Pronger and Blake do have some offense but aren't the skating defensemen to do this. Pronger made nice breakout passes, Blake in his younger days could come in with a great shot and had good offensive instincts but I wouldn't call either one of them end to end rushers.
This left McCabe who was just there because he was killing it on the power play. Regehr and Foote are stay at home guys anyway. Redden was alright, but certainly not a rusher that you need that can replace Niedermayer. Bouwmeester certainly had the speed but he just never lived up to the hype of being able to rush the puck at an elite level at the NHL level.
Yeah, they needed Boyle there. He's your best replacement for Niedermayer on that big ice. Jovanovski as well was injured but while he had his moments offensively he wasn't a classic rusher. It's Boyle at that point. And even then it's still pretty early on in his good years.
To tell you the truth though, on paper that Canadian defense still should have gotten the job done. They had good defensemen. Even missing Niedermayer and his rushing the puck skill was a blow sure, but they still should have had more than enough to make up for it.