According to a preview clip on NBC's The Office website, Jim had dumped Karen and left her "crying by a fountain in New York City" following the events of Season 3.
After being dumped by Jim in "Fun Run," Karen explains to Jim that they will still have to learn to co-operate as co-workers. However, the next morning, Jim discovers that Karen's desk is empty, and that she has left the office for good. The writers have stated that she will appear in two episodes in season four to tie up her storyline. According to TV Guide's "The Ausiello Report," these appearances will feature Karen at her new workplace. E! Online's Kristin Dos Santos reports that the sixth episode of season 4, titled "Branch Wars," is being filmed at Dunder Mifflin's Utica, New York branch, where Karen is presumed to be working.