3) In the books, Wormtongue does NOT kill Saruman during the confrontation at Isengard. The Ents eventually allow Saruman to depart, believing that he is no longer dangerous. When the hobbits return home to the Shire they find it under martial law, ruled by a 'big chief' known as Sharkey. Sharkey turns out to be Saruman, but the hobbits led by Merry and Pippin overturn his rule and throw him out. There is a final confrontation between Saruman and Frodo, in which Frodo spares Saruman's life. As they depart Saruman curses Wormtongue, and Wormtongue snaps and turns on him, stabbing him to death. Wormtongue is in turn shot with arrows from several hobbit archers and dies.
In the film, this whole end sequence in the Shire is cut out, and Wormtongue kills Saruman at Isengard for reasons that are not altogether explained. I assume this was done because even with this much abridged ending, the film is still very long for the cinema. Indeed, I think in the original cinema version of Return of the King, the scenes with Saruman and Wormtongue were cut completely; they appear only in the later 'extended' version