Some thoughts on roster construction over the next few years:
(2013) Only two players of significance will be FA's this offseason: Edwin Jackson and Adam LaRoche. The only other pending FAs on the active roster are Mike Gonzalez, Mark DeRosa and Chad Tracy, who could all be re-signed or easily replaced by signing another FA or promoting from within. Chien Ming-Wang's contract also comes off the books. Sean Burnett has a club option for next season at around 3 million that will almost certainly be picked up.
I expect LaRoche to be let go. He's played well this season but the team has tremendous depth at the position in Mike Morse and Tyler Moore, not to mention a former prospect in Chris Marrero. Those players need room to play and to develop, and the drop-off in value from LaRoche to Moore is not worth Laroche's salary and limiting Moore's development. Letting Laroche go creates a roster spot for Moore, Corey Brown, and Lombardozzi to rotate through absent injury.
Edwin Jackson could be re-signed, but I expect him to leave. He has performed well this year and is deserving of a multi-year contract somewhere. But I don't see Rizzo giving him a big multi-year deal to be a #4 starter. He'll get paid more to go to another team as a #1 or #2 guy. To replace Jackson, Rizzo could go after a guy like Grienke, who he's known to covet. Or more likely, he will sign a cast-off (e.g. a Chris Young or a Joe Saunders) and have them compete in spring training. In that scenario, Detwiler becomes the #4, and guys like Lannan, Yunesky Maya, perhaps even Gorzelanny and/or Stammen compete for the fifth spot with whoever is added.
(2014) The main FA in 2014 will be Mike Morse. Sean Burnett and Kurt Suzuki (the latter with an expensive option) are the only other valuable commodities whose contracts run out that year. The several other FAs are replaceable role players: Tom Gorzelanny, John Lannan, Yunesky Maya, Jesus Flores.
I expect Morse to leave after the 2013 season. If Tyler Moore and Corey Brown continue to develop, they will be more attractive options than a then-32 Morse in 2014. Expect Morse to move to the American League where he can DH at least part of the time.
Whether Sean Burnett and Kurt Suzuki continue on with the club will be determined by their performance in the next year and a half.
Summary: Over the next two years, only two key position players will become free agents, and both--LaRoche and Morse--are natural first basemen who will command high salaries. Expect both to leave. The replacements for these players are likely already on the roster in Tyler Moore and Corey Brown.
Several bullpen arms will become FAs, but the only top arm is that of Burnett. All including Burnett could be replaced without difficulty if they choose to go elsewhere.
Edwin Jackson's spot is the only place where a big FA signing is possible over the next two years. There is no obvious replacement for him in the minors, although the team does have an adequate replacement in Lannan.
In other words, the team is essentially set for the next three years.