It will continue to be replacement by committee for the Rangers as they try to fill the irreplaceable void left by the injury to Ryan McDonagh. The Rangers best skater and stalwart defenseman missed his second straight game in Saturday night’s 3-2 loss to the Senators at the Garden, with coach Alain Vigneault calling him “day-to-day” with his left-shoulder injury sustained on a brutal hit from the Canucks’ Alexandre Burrows in Vancouver on Tuesday. So that left Vigneault with another game in which he had to rotate his cast of defensive pairs, constantly switching guys on and off the ice with different partners, everyone besides Dan Girardi and Marc Staal being forced at least at some point to play his unnatural side. Yet, as could have been expected, the leaders in ice time remained Girardi (26:11) and Staal (23:06), though a close third was John Moore (21:33), who was playing just his second game back after missing six with a concussion. “First of all, I don’t think you can replace a guy like Mac,” Moore said before the game. “He’s a guy that plays in all situations, he’s one of the premier defensemen in the league. So I think it’s a challenge for all six of us in the lineup to raise our level.” Moore scored a goal in his first game in Colorado, and almost got another one on Saturday, firing a long slap shot early in the second period that was deflected by Benoit Pouliot and then finally by Mats Zuccarello before going in, cutting Ottawa’s lead to 2-1.