Ultron will undoubtedly be "defeated" in the upcoming Avengers: Age Of Ultron, which is out in May of this year. That said, in the comic books at least, Ultron has a habit of coming back - usually due to the fact that he is essentially an electronic consciousness. The Avengers will destroy his upgraded body somehow in the final battle of the movie, but his consciousness will surely still exist. Therefore, he could well build himself a new body and jet off into space in one of the movie's mid or post-credits scenes. In Phase 3, therefore, he could well to return to the big screen with an army - perhaps the Phalanx, a race of mechanical aliens - and pose a threat to some of the space-based heroes in the Marvel Cinematic Universe. Watch out Guardians Of The Galaxy, Nova Corps etc.
