The GOP has a chance if Coakley is nominated. And she may well be nominated. She's a poor candidate that gives the GOP an opening if she is nominated.
But who do Republicans have to put up against her? I doubt Charlie Baker could beat her, considering he couldn't win in 2010.
Massachusetts is SO Democratic that the GOP always nominates candidates who could well be Democrats in other states. This gives the general election something of a non-partisan tone where the voter can concentrate more on individual personalities. A Massachusetts Democrat can vote for a Republican they might like without thinking they've signed off on the platter of conservative social issue positions they abhor.