Ryan Dempster, Randy Wells, Tom Gorzelanny and Carlos Silva may not be utterly dominant, but they will provide the Cubs with certainty this winter and quality innings next season. If healthy, those four starters should account for most of Chicago's rotation in 2011. They won't be enough, of course. The Cubs will need a fifth starter, too and while Carlos Zambrano could continue improving and fill that role, it may not be that simple.
The Cubs will likely consider trading Zambrano but their offseason doesn’t hinge on making a trade, like it did a year ago when they flipped Milton Bradley for Silva. Zambrano's season reached a low point when he got into a dugout shouting match with Derrek Lee, but he has pitched well since returning from the restricted list. He has a 2.25 ERA with nearly a strikeout per inning since the end of July, but is walking more batters than usual, which is something, considering Zambrano has a career walk rate of 4.1 BB/9.
If the Cubs hold onto Zambrano, they probably won’t be in the market for starting pitching, since they have other internal candidates who could fill in. But if they trade Zambrano - and it wouldn't be easy given the $17.875MM he makes in 2011 - the Cubs would have an empty rotation spot and could consider signing a free agent starter. The caliber of that starter might depend on the savings from a Zambrano deal.
But even if GM Jim Hendry doesn't like the options on the free agent market, he has a number of potential starters in the organization. Jeff Samardzija and Casey Coleman could contend for a rotation spot if one opens because of a trade or injury. Samardzija has a high walk rate in Triple A this year (5.4 BB/9), so he'd probably have to show the Cubs that he can limit free passes. Coleman has posted a 5.81 ERA in the majors and has walked more batters than he has struck out, but his Triple A numbers were much better (4.07 ERA, 2.7 BB/9). Baseball America noted before the season that Coleman has a good feel for pitching, which isn't surprising since his father and grandfather pitched in the majors leagues before him.
Sean Marshall and Andrew Cashner are both contributing out of the ‘pen now, but the Cubs could stretch them out if necessary. Marshall has been one of the National League's best left-handed relievers this year, but he started games regularly from 2006-09. Cashner's used to starting, too; he had a 2.05 ERA as a starter in the upper minors this year before the Cubs called him up.
Thomas Diamond started three games for the Cubs this year, but has struggled to limit walks. The former first rounder has faced just over 100 batters in his major league career, so it seems more likely that he'll pitch in the minors or the bullpen for now. Chris Archer, who doesn’t turn 22 until later this month, posted a 2.34 ERA with 9.4 K/9 in the minors this year, but he has appeared in just 13 AA games, so he will need time to develop.
Remember that, in all likelihood, the Cubs will have a new manager by Spring Training. That means the fifth spot in the rotation depends not only on the team's offseason moves, but on their new manager's preferences. It's too early to predict how it will all unfold, but we can safely say that Zambrano appears to be the leading candidate to be the team's fifth starter. If the Cubs trade him, they may consider free agents or turn to internal options like Coleman, Samardzija, Marshall and Cashner.