Well, he does have to trade someone.
Chances are we use a 7 man bullpen, as it is the standard, and frankly, one area the Sox have allowed themselves to get weaker this offseason, With our 5 man rotation, that leaves 12 pitchers.
With 9 starters, that leaves the Sox with 4 bench spots. Pearce, Holt, Nunez and one backup catcher. One.
If Pedroia is on the DL, then we can fit both. But what if he isn't? If he can play, he will and he should. And if he can, someone has to go. Also, I don't think any of these 5 candidates for the bench have any options left. Sources disagree as to whether or not Holt has one, but it really doesn't matter. The Sox are NOT going to send Holt to Pawtucket to keep Swihart on the roster.
Swihart is probably the likeliest candidate to be dealt, but he isn't going to bring much back. The Sox have tried that already and it's not like he has done much to make any GM re-think his opinion of Blake. Tht leaves the last option of simply releasing Swihart, which is certainly a possibility.
But if Pedroia is on the DL, look at the Sox bench, They would have a 1B in Pearce or Moreland (whichever one was not starting ), a 2B/3B player in either Holt or Nunez (whichever one was not starting ), a backup catcher in Leon and ... another backup catcher in Swihart who has had limited experience with even more limited success at other positions. Do we want a bench with maybe a reserve outfielder? Or a defensively capable SS?
JD Martinez right now is the fourth outfielder, but that doesn't help in-game replacements. If Cora ever pinch hits for, say, Bradley, do we his glove replaced in the field by Holt/Nunez/Swihart? Or if Bogaerts has to leave a game, who covers SS?
I know this bench worked out fine last year, but that doesn't mean it can't be improved upon and made more capable. Defense is the primary expectation from bench players, since bench players who can hit are typically starters.
Remember when Cora was forced to go deep into his bench in Game 3 of the World Series and we had a horrific offensively-challenged lineup featuring both Vazquez and Swihart? Like many Sox fans, I watched that whole game. But there was very rarely an inning where the Sox were coming up when I got excited about their chances to score. And that was a game in an NL park, where we did have one of our regulars on the bench and we still wound up with both Leon and Vazquez in the game for a long, long time...