It's impossible in the salary cap era to replace a #1 center who just won the scoring title last season.
Unless you're the Pittsburgh Penguins and you just so happen to have two #1 centers who have won scoring titles and league MVP's in the past.
There's no doubt that if Evgeni Malkin has suffered a serious head/neck injury, the Penguins season is dead in the water. Just as it was two years ago when Malkin and Sidney Crosby both suffered season ending injuries. Teams just can't win it all when they're down such a huge piece of the puzzle.
That said, Pittsburgh is still a really solid and very capable hockey team even if #71 or #87 are out of the lineup. We know Malkin will miss tomorrow's game against the Tampa Bay Lightning, if he has to miss more (and he almost certainly will) where do the Pens go from here?
Move Neal up with Crosby
James Neal was acquired with the idea to play with Crosby, but Crosby was hurt and Neal has had undeniable chemistry and results playing with Malkin. Neal also struggles without having a great playmaking center, always has since his days in Dallas when he scored goals when he played with Brad Richards, and didn't when he was apart. The same held true in Pittsburgh when Neal scored just 2 goals in 27 games (regular season and playoffs combined) when Neal had Jordan Staal and Mark Letestu as his centers.
Putting Crosby with Neal is a no-brainer. That leaves one of either Chris Kunitz or Dupuis to round out the line. Personally, to give the second line a little more scoring and playmaking punch, I'd keep Dupuis with Crosby and put Kunitz on the second line.
Big chance for Sutter and Jeffrey
Without Malkin the Penguins need someone to step into the second line center role, and the best candidates are Dustin Jeffrey and Brandon Sutter. Jeffrey's been mainly a healthy scratch, and while he probably isn't a true productive top 6 player, he does have the hands and ability enough to think the game to be a decent band-aid.
Sutter has played in more of a third line role throughout his career, but he's also a guy who's scored 20 goals in a season at the NHL level when he was with Carolina. Sutter has the skill to be a decent option there too.
Youngsters need to make mark
There's still an opening for either Beau Bennett or Zach Boychuk to make their mark. Withou Malkin, the team will need goal production and some more power play time will be opened up. Both Bennett and Boychuk has some skill, but neither has made a huge impact in the NHL yet. If there was ever the time for an opportunity, it may be right now.
Without Evgeni Malkin, the Pens don't pack nearly the scoring punch and the opposition can load up their best checking and defensive pair to try and shut-down Crosby/Neal without much worry of another line being too dangerous. That's a disadvantage, but an unavoidable one.
Here's how we see the lines shaking out until Malkin is able to return
Dupuis - Crosby - Neal
Kunitz - Sutter - Bennett or Boychuk
Cooke - Jeffrey - Kennedy
Glass - Vitale - Adams