As much as I maintain that the Cubs were a good team going into the season, it's very unlikely for any team to pick up 12 games in a half season. It happens from time to time, but not many.
So lets look at the the lineup for next year. Of the positions that will be the same
3B - Ramirez (I think the Cubs have an option they will pick up)
SS - Castro, C - Soto, LF - Soriano, CF - Byrd, 2B - Barney
The starting pitching staff will probably feature the same 5 guys it had going into this year. The most likely one to be gone is Zambrano.
The openings are in RF and 1B. Internally, the Cubs best OF is probably Brett Jackson, but he's currently in Double-A and probably won't be ready. Not much at first at all. The Cubs might keep Reed Johnson around but I don't like that as an everyday option.