Whole season of Victor Martinez plus a reasonable solution to the corner infield issue. (Maybe even Lowell himself playing 1B ) and the Sox don't lose nearly as much offensive production as you state. As i posted before, this year's Sox were superior in almost every offensive category to the 2007 WS winning team, but their pitching was inferior. Losing Bay is not such a big deal. Getting Lackey and a healthy Dice-K is a big deal.
If anything, the Sox have the flexibility to get a bat if they truly need it, but the rotation is set. Some people may not like to hear this, but objectively speaking, the 2010 version of the Red Sox, health permitting, will be much better than the 2009 version.