The movie is still a go. Its a question of when, not if.
Howard Gordon came out in past few days confirming that the movie will absolutely not be a prequel. That the film has been in the pipeline for a while, but the film pitch in its current form will mould around the series finale and the finale will not lead towards the film.
24 has always used the same organic process. This wouldnt work for a series like Lost, but benefited 24 greatly. At sometimes the series was brief, on the spot and question plausibility, but I do appreciate where this writing style has lead 24.
After just watching the series finale -- wow, 24's last hour was its finest! Awesome episode!