One could say the same about Man U if either Berbatov or Tevez got injured at the moment...
We beat Man U without both Torres and Gerrard in the team at Anfield, so I'm not too concerned, especially as we are where we are now without having Torres for most of the season so far. Lucas is much more effective when he is played in the role behind the front striker and I think he can cover for Gerrard if needed, as he has done in key games when he's replaced him as sub already this season.
Babel has been pretty bad this season, but he's been played down the left wing mainly to keep him in some kind of match fitness. Would imagine we'll see more of him in the centre again soon as Rafa has been known to keep young prospects simmering to release them at tired defences at the end of the season. There's some useful players who are being blooded by Rafa who can do a job - you mention N'Gog, but there's also El Zhar. Yet my money is on Pacheco to be a huge star at some point soon. That lad can play and is exactly the type of 'Aimar' player who can unlock defences.