BOSTON -- The Boston Bruins have stared down perceived disasters before and triumphed.

Shortly after defenseman Dennis Seidenberg left their game against the Ottawa Senators with an injury last December, the Bruins learned he was lost for the season and needed surgery to repair the anterior cruciate and medial collateral ligaments in his knee. Less than a month later, a couple of injuries ended defenseman Adam McQuaid's season.

The Bruins still won the Presidents' Trophy with 117 points despite missing two of their most important defensemen.

With their regular season opening against the Philadelphia Flyers on Wednesday at TD Garden (7:30 p.m. ET, NBCSN), the Bruins again are dealing with the loss of one of their reliable veterans on the blue line, but this time on a permanent basis.

Defenseman Johnny Boychuk was traded to the New York Islanders on Saturday for draft picks. The trade was made for salary-cap reasons; general manager Peter Chiarelli said, "Arguably this doesn't make us better now."

The absences of Seidenberg and McQuaid might have been too much for the Bruins to overcome when they lost to the Montreal Canadiens in the Eastern Conference Second Round. But their experiences from last season should help the Bruins at the outset of the 2014-15 season.

"You know a similar thing happened last year when [Seidenberg] went down and [McQuaid] went down. Everybody's freaking out that we're in trouble," Bruins defenseman Torey Krug said. "I thought that the group of guys that we had in there [last season], the committee that filled those spots, did a great job. We ended up winning the Presidents' Trophy. I think it's a similar thing. I think we're excited to hopefully disprove all those things. And we've always been a group that's always showed up when we have to."

Just back from a two-day team-bonding trip to Vermont, the Bruins still are dealing with some of the emotions that resulted from the Boychuk trade. However, coach Claude Julien is confident the surprise and disappointment that came from the trade will be gone when the puck drops Wednesday.

"I think the players are excited to start the season," Julien said. "Those things, at first they sting and then day-by-day it gets a little better," Julien said. "But our guys have moved on. It doesn't mean you forget about a friend. But we've moved on. We know we have a job to do and we have business that's more important ahead of us. So that's how we feel, and I'm the same way. I'm excited about the season to begin. I saw some good things in training camp. I guess a lot of young players auditioned for those open spots, and we're kind of finalizing that. But it was some great competition, and again we have an opportunity to have a real exciting and competitive team. So what coach wouldn't be excited about that?"

The Bruins are three years removed from winning the Stanley Cup in 2011. The core of the team, including defenseman Zdeno Chara, goaltender Tuukka Rask and centers David Krejci and Patrice Bergeron, remains intact; the Bruins are committed to those players through the end of this decade.

Much of the supporting cast from the 2011 championship season and the 2013 Stanley Cup runner-up season also remains in Boston. There's no telling how much longer, though, that will be the case.

Boychuk can be an unrestricted free agent after the season, and Chiarelli said that based on the market and the NHL salary cap he knew he wouldn't be able to re-sign the defenseman. Chiarelli also has other players heading toward free agency after the season. Centers Carl Soderberg and Gregory Campbell, forward Daniel Paille and defensemen McQuaid and Matt Bartkowski can be unrestricted free agents; defensemen Dougie Hamilton and Krug, forwards Reilly Smith, Ryan Spooner and Matt Fraser and goaltender Niklas Svedberg can be restricted free agents. Like Boychuk, not everyone will be able to stick with the Bruins.

Roster uncertainty of that sort hasn't been seen around the Bruins since at least 2011. Perhaps that uncertainty will result in greater focus and determination.

"You want to make sure that you're taking care of business because you're fighting for a job, not only this year but for the future as well," Krug said. "So it's very important that you focus on yourself and you don't get too crazy and you just come to work every single day ready to go."

Said Smith: "I guess if you think of it like that, there can be that little bit of urgency that this is the year to get it done. And we still have a great group here even with recent transactions. To make the most of it you've got to come out of the gates fast. That's one thing we're focused on."

Uncertainty around the Bruins isn't limited to contract status. Campbell hasn't been through a full practice since the start of training camp and is doubtful to play Wednesday. Krejci sustained an injury in the last preseason game and his availability for Wednesday was unknown after practice Tuesday. Forward Milan Lucic still is working his way back from offseason wrist surgery, and Smith and Krug got a late start to camp after signing Sept. 29. And forward Loui Eriksson had a rough training camp.

Even though training camp officially is over, there still are ongoing battles for lineup spots. Spooner, Fraser and Bobby Robins have made the team as new faces. At least three of the seven defensemen are competing for regular spots in the lineup.

Despite the changes and uncertainty, the Bruins expect to be successful once again.

"I usually have high expectations," Bruins president Cam Neely said. "We had a successful regular season last year, and as we all know we fell short of what we wanted to accomplish in the playoffs. I know the guys are hungry. We have a lot of returning players that want to improve upon what we did last year. I think based on what I've seen and the way they're talking, I think they're excited about getting the season going. But the expectations are high."