Not a big loss. All he is anymore is leadership and a voice in the room.
And he still provides that even though he is injured
The biggest loss is the 60% faceoff percentage.
In their last game against Minny, the Canucks got destroyed in the circle. It didn't cost them the game, but it easily could have.
As someone already pointed out, having a reliable center to take a defensive zone faceoff in the closing moments with a one-goal lead is huge. The ideal thing (which the Canucks were actually doing before losing Manny) is to have him and Lapierre, so whoever is on their strong side can take the draw, or step in, in the event the other guy is waved out.
I'm not all that keen on having Hank take the draw in that situation, which leaves the team with Lappy, Schroeder or Kes when he returns. Kes has been good in the past, but I think he'll have trouble initially after missing so much time.
In my mind, Manny's situation changes the Luongo trade dynamic a bit. I believe that Gillis might now be looking at a defensive center (preferably a lefty) with good faceoff numbers, as part of the package.