Here are the extras on the recently announced US DVD release of The Break Up:
"Universal Home Video are to release the The Break-Up which stars Jennifer Aniston and Vince Vaughn on 17th October 2006. The DVD will provide a "what might have been" alternative ending, 20 minutes of deleted/extended scenes and outtakes, a "Three Brothers: A Tour of Chicago" behind-the-scenes featurette introduced by Vince Vaughn, an "Improv with Vince Vaughn and Jon Favreau" featurette, a "In Perfect Harmony: The Tone Rangers" featuette where John Michael Higgins shows you what it takes to be a Tone Ranger, a "The Making of The Break-Up" featurette, a commentary with Vince Vaughn and Jennifer Aniston, and a second commentary by Director Peyton Reed."
So it does look like there was a different ending to The Break Up!