A bit about my lineup, and the assumptions I used, before I did into the numbers. For full time players I simply used their weighted means for average, on base percentage, and slugging for the table below. For positions that I expect to be shared I used a baseline of 550 at bats for a position total and weighted overall stats as necessary. To keep things relatively simple, I didn't include players like Lowrie, whose playing time is uncertain for 2010. The positions with multiple players are: 1B (Kotchman 450 AB, Martinez 100 AB), RF (Drew 450 AB, Hermida 100 AB), LF (Cameron 450 AB, Hermida 100 AB), and C (Martinez 450 AB, Varitek 100 AB). With those playing time splits, I give to you the offense of the 2010 Red Sox:
As you can see, the projected 2010 offense should actually be slightly better than the 2009 offense. Of course, these estimates are likely a little high. If I could guarantee that Papi puts up an .870 OPS I'd jump at the chance. I imagine Theo would too. I also haven't included any of the marginal players that a team always plays during days off or minor injuries. Jed Lowrie would substantially weigh down a team OPS with his career .685 OPS.
According to the Baseball Musings lineup calculator, the lineup above would score 5.718 runs per game. It isn't quite right to simply lump the players together into one, but for our purposes it is good enough. A team that scores 5.718 runs per game would score 926 on the season. Interestingly, according to my very simplistic model, the offense with Kotchman would be better than it would be with Beltre, thanks to Beltre's extremely poor showing in 2009. That doesn't factor in defense though. Although this off season is being presented as a lateral move at best with regard to scoring runs, I think the fact that the Red Sox shortstops were so unbelievably bad last year makes it possible to match the offensive production even with the loss of Bay.