I think they would have to run the national feed (I'd said W1 but I think it's ESPN Radio).We'll see.
Portland Press Herald, 10-22-13:
"Red Sox radio listeners around here will be deprived of their regular radio team because ESPN’s contract with Major League Baseball says the network has exclusive rights to broadcast the World Series around the country. The only exception is that the “flagship” radio station of each team in the World Series can use its own broadcasters to broadcast the games in its immediate area (emphasis mine).That means the Boston station that employs O’Brien and Castiglione, WEEI (93.7 FM), will still broadcast the World Series games and still use O’Brien and Castiglione. And since the station’s signal is fairly powerful, some listeners in southern York County may be able to hear it.
But most fans across New England listen to WEEI’s Red Sox broadcasts on a network of more than 50 affiliate stations"