I’d think Pedro grabbing his ankles and asking Jeter to be hid daddy on the mound infront of 55k screaming praying fans would be enough to make Bean Town into a smouldering pit of ash…But as for your OP, Yeah, I believe beating the Yanks would be the bigger tumult for Boston than them actually winning the WS. And this coming from a Yankee fan.
Just Boston? I think that would signify a rift in the time/space continuum that could never be closed, allowing the Demon Gods of Rylean IV to cross into our plane of existence. Mighty rivers would reverse their course, watches would run backwards and the lamb would lie down with the lambaste. Traffic would flow smoothly; Bush and Kerry would say nice things about one another. It would be total chaos.
Bigger than beating the Yanks? How about this scenario, unlikely as it is:
Imagine a Yank hits the ball, a potential playoff clinching hit, deep into right field. The Sox right fielder runs backward and extends his glove to catch the ball…but is unable because he’s beaten to the ball by some overzealous fan in the stands.