EA has responded to the letter with guns fully drawn, saying, "We doubt that Activision would try to sue. That would be like a husband abandoning his family and then suing after his wife meets a better looking guy." We've got two words for you EA: Oh (and) Snap!
Savvy Joystiq readers may remember that this isn't the first time Activision has made efforts to block progress on Brütal Legend's inevitable release. Back in October, an unnamed source at Double Fine was quoted as saying Activision was "blocking the process" (of being added to EA's publishing roster), just months after being dropped by the publisher. Though it's the weekend and we likely won't hear anything until Tuesday (what with President's Day and all), we've put in word to EA and Activision for comment and will update accordingly as news comes in.