We can assume that the Twins would’ve opened the season with a rotation of Johan Santana, Scott Baker, Kevin Slowey, Boof Bonser and Livan Hernandez. Let’s run with this idea.

This season for the Twins, Glen Perkins replaced Scott Baker in the rotation on May 10, because Baker had gotten injured. Perkins has remained in the rotation since.

Then, when Baker returned to the rotation, he replaced Boof Bonser, relegating Bonser to the bullpen.

Then Francisco Liriano replaced Livan Hernandez at the beginning of August.

Let’s assume that the Twins were wedded to Hernandez through the end of July, no matter what. After all, they could have called up Liriano earlier – Liriano began dominating in triple-A on June 10.

So if the Twins had Johan Santana the entire year…

When Scott Baker gets hurt, Nick Blackburn would replace him on May 10, not Glen Perkins, since we can assume that Blackburn was ahead of Perkins on the Twins organizational depth chart. Therefore, Blackburn would have made 25 starts, not 32. Meaning Blackburn would have pitched 146 innings (25 starts x 5.84 innings per start, which is what he’s averaged this year), rather than 187.

Then, we can assume that Baker would once again replace Bonser in the rotation when he returned on June 10.

Would Perkins have ever cracked the rotation? His only hope would have been if the Twins decided to give up on Livan Hernandez and replace him with Perkins. The fact that they left Liriano in triple-A for nearly two months while Liriano pitched well and Hernandez pitched terribly suggests that they would not have been inclined to insert Perkins over Hernandez, either. Therefore, we can assume that Perkins would’ve never made it into the rotation, and would’ve spent the year in the bullpen.

Nick Blackburn would’ve been inserted into the rotation when Scott Baker got hurt, and then would’ve stayed in the rotation when Baker came back – essentially, Blackburn would’ve played the role of Glen Perkins. In this scenario, Perkins would never have cracked the rotation.

So the 32 starts that Johan would have made were actually split between Blackburn and Perkins – Blackburn made seven (the additional starts before Baker got hurt), and Perkins made 25.

How might Johan Santana have fared in the AL? Well, the AL is better than the NL this year, and Shea Stadium is a pitcher’s park.

First let’s take Santana’s raw ERA of 2.64 and park-adjust it. Interestingly, it appears that the Metrodome played as a pitcher’s park this year, a little more even than Shea Stadium. It was actually more difficult to homer in the Metrodome than in Shea, and both parks severely depressed singles. Given Shea’s tendency to be more of a pitcher’s park over the long-term, let’s call this a wash (even though I believe Shea is probably still more difficult to hit in than the Metrodome).

Therefore, the only adjustment necessary is a league adjustment. There is a 1% difference in the average AL ERA (4.29) and average NL ERA (4.33), but we can assume that there is approximately a 6-7% difference in league quality overall. This was discussed in Baseball Between the Numbers a few years ago, and the difference in league quality hasn’t curtailed much (if at all) since then. Let’s say that Johan’s ERA would rise 6% by virtue of being in the AL. That would take his 2.68 ERA and bring it up to 2.84. That seems reasonable enough.

Essentially what this all means is that the Twins would have 32 starts from Johan, totaling 225 innings with a 2.84 ERA, meaning Johan would’ve given up 71 runs in those 225 innings.

Remember, his starts would have come at the expense of Blackburn and Perkins. In his seven additional starts, Blackburn would’ve pitched 41 innings (he averaged 5.84 innings per start), and allowed 19 runs. Perkins would’ve pitched 146 innings, allowing 73 runs. This is the production that Johan would have replaced – 187 innings, and 92 runs. But Johan has pitched 225 innings, so he also would have replaced an additional 38 innings from the bullpen. The Twins’ bullpen has a 3.93 ERA, so in those 38 innings the Twins’ bullpen would have allowed 17 runs. So in the 225 innings that Johan would have pitched, he would have allowed 71 runs. Instead, those innings were split between Blackburn, Perkins, and the bullpen, and they combined to allow 109 runs.
 
                  IP     ER                          IP    ER      
Johan    225    71    Blackburn    41    19      
                                   Perkins       146   73      
                                   Bullpen        38    17      
                                   Total            225   109     


Therefore, we can say that Johan Santana would’ve saved the Twins 38 runs – and, in reality, he probably would’ve saved them more, because his presence would’ve knocked the worst pitcher out of the bullpen (replacing that pitcher with Nick Blackburn first and Glen Perkins later). Therefore, we can conservatively estimate that Johan Santana’s presence would’ve been worth at least four wins to this current Twins team, assuming similar performance by everyone else (and similar behavior from the management in terms of who replaces whom, and when). Considering the Twins are 0.5 games behind the White Sox, those four wins would mean a heck of a lot.

Furthermore, if the Twins had never made that deal, they wouldn’t have had Carlos Gomez and his abysmal offensive production (granted, Gomez is excellent defensively in center field). It’s unlikely that the Twins would’ve managed to find an even worse offensive player to replace Gomez (who hit .258/.297/.354 in 559 at bats), and it’s quite possible that they would’ve received a lot more production. Heck, Gomez’s VORP this year was -2.4, meaning that he was worse than a replacement player. Even if you take Gomez’s excellent defense into consideration, his production was barely better than a replacement player, so all the Twins would have to do in order to improve upon his production was find a slightly-better-than-replacement-player to play in center field.

Of course, hindsight is 20/20. PECOTA projected the Twins to win 73 games, and while that seemed slightly low, I thought the Twins would be in a battle with the White Sox all year…for third place all season. While I was skeptical of the return, I agreed with the Twins’ decision to deal Johan before the season, because I thought that that was when he would have the most value, and I thought the Twins didn’t have a chance of competing. Therefore, I do not fault Bill Smith’s decision to deal Johan.

But it’s still interesting to consider where the Twins would be if they still had him.