Here are extracts from Scott Bettencourt's six-part article called "TIMELINES: JOHN WILLIAMS" which was published on FSM website in 2007:
1974: Williams was originally announced to score Robert Altman's gambling drama, CALIFORNIA SPLIT, which featured his actress wife Barbara Ruick in a supporting role. Ruick died unexpectedly of a cerebral hemorrhage during the filming and Williams left the project, though despite his personal tragedy (which inspired his violin concerto), he kept working.
1976: Around the same time, Williams was announced to score Michael Winner's Satanic horror film THE SENTINEL, but wisely backed out at the last moment -- reportedly due to illness, but probably it was simply good sense, as anyone who has seen Winner's film can attest to. It was the first of many incidents were Williams would back out on a project that turned out to be a disaster.
1979: Williams was also announced to score two science-fiction films that proved to be expensive disasters. QUINTET was a bleak post-apocalyptic drama from Robert Altman, with memorable visuals but little in the way of narrative excitement or emotional involvement. It would have been fascinating to see what Williams could have done with such dark material -- especially since Williams' previous collaborations with Altman were so musically unusual -- but Williams left the project, and the striking score was written by Tom Pierson (who was later the music director for Altman's Popeye).
METEOR was a big-budget disaster film with a George Pal flavor, but the troubled project ended up with a lengthy post-production period as the effects were redone (and still came out surprisingly cheap looking). Williams' departure may have been due to the scheduling delays, but it proved to be a commercially wise choice. Laurence Rosenthal's score had some fine passagea, especially his soaring main theme, and, ironically, unlike Dracula and 1941, his score was short-listed for the Oscar (in the last year of the Original Score shortlist) -- it was a rare year that Williams had new scores but no Oscar nominations.
1980: Around this time, Williams bailed on two particularly infamous flops. Michael Cimino's visually staggering HEAVEN'S GATE had Williams attached at one point (and Morricone was also considered for the project), but Williams wisely departed (leaving The Missouri Breaks as his final Western score to date), and Cimino went in a markedly different direction with the young composer David Mansfield, whose folksy score proved to be one of the film's most popular elements; he went on to score three more features for the controversial director.
INCHON was an epic about a pivotal battle of the Korean War, financed by Reverend Sun Yung Moon, with Terence Young (From Russia with Love, Wait Until Dark) directing an all-star cast headed by Laurence Olivier as General MacArthur (no, really). The film's U.S. opening was delayed, as major subplots and characters were cut out completely, and it was released very briefly in the fall of 1982 before disappearing completely (as far as I know, it has never been released on video or cable). Jerry Goldsmith ultimately provided the score (which gave him the rare opportunity to write a second theme for MacArthur), a lively work which is practically the only thing about the movie that has survived.
Considering how great a part of Superman's success his score was, it was only natural that he'd be invited to score SUPERMAN II, much of which was filmed concurrently with the first Superman (though Richard Lester replaced Richard Donner for the completion of the film), but ultimately the film was scored by Lester's regular composer Ken Thorne, basing virtually his entire score on Williams's themes and cues (effectively if unimaginatively). One of Superman's producers has claimed that Williams met with Lester about scoring the film but had such a negative reaction to the director that he turned the job down. Considering how famously easygoing both Lester and Williams are, this scenario is less than plausible -- it's far more likely that the Superman producers simply didn't want to pay Williams' fee (the Brando footage shot for Superman II was deleted for similar financial reasons, while Lester has said he worked on the Superman films mostly to get money owed to him by the producers from their Musketeers films).
1994: In the mid-90s, there were rumors that Williams was considering retirement (his leadership of the Boston Pops ended in 1993), and he didn't score any new films in 1994. He was originally announced to score Mike Nichols' offbeat werewolf thriller WOLF (which would have made a nice companion piece with Williams's Dracula and The Witches of Eastwick), but Williams ultimately left the project and Ennio Morricone wrote a typically striking score.
1999: Williams was originally announced to score Chris Columbus' megabudget project for 1999, the sci-fi comedy drama BICENTENNIAL MAN, with Robin Williams as a robot fighting for his rights as a sentient being, but the film ended up being scored by James Horner (and was a rare commercial failure for the director). Instead, Williams scored his only (to date) film for director Alan Parker, the underrated adaptation of Frank McCourt's best-selling memoir ANGELA'S ASHES.