The infamous Happily Ever After version of Shakespeare's King Lear by Nahum Tate. The 1681 rewrite (which Tate boasted "rectifies what was wanting in the Regularity and Probability of the Tale") ends with the good guys surviving, Lear regaining his throne, and Edgar and Cordelia marrying. It proved so popular with Restoration audiences (who hated Shakespeare's Kill 'em AllDowner Ending—purely his own invention and diverging drastically from his source material, the Historia Regum Britanniae, in which the legendary king's story has a cheerful conclusion) that it completely eclipsed Shakespeare's King Lear for the next 150 years, enjoying hundreds of productions, while the original Lear languished in obscurity and went all but unperformed. In the 1830s reverent fans of the Bard began to restore Shakespeare's original ending to performances, and the Tate version gradually fell out of favor, increasingly derided by Victorian critics as sentimental and trite. Since the start of the twentieth century, the Tate play has only been revived a few times, and then only as a quaint historical curiosity. It's mostly remembered today as one of the earliest and oddest examples of Disneyfication.
Vaudeville (a series of unrelated acts, such as musicians, dancers, comedians, trained animals, magicians or acrobats), was one of the most popular types of entertainment in America for several decades between the 1880s and the 1930s. It waned due to the arrival of radio and the Rise of the Talkies, and is today remembered mainly for having been the breeding ground for many of the talents of The Golden Age of Hollywood.
Same applies to its British cousin, the music hall, where performers typically mixed comedy and musical performances. Once England's predominant source of middlebrow entertainment, music hall's popularity waned in the 1920s and '30s with the rise of more sophisticated comedy and musical acts (not to mention film and television), though remnants lingered into the '60s. Its legacy is mixed, remembered either nostalgically for its influence on British culture, or as an anachronistic remnant of Britain's imperial past (as in John Osborne's The Entertainer).
Circus almost met this fate in North America in the late 20th century thanks, again, to the rise of TV; by the mid-1980s even Ringling Bros. and Barnum & Bailey had been reduced to gimmicks like "The Living Unicorn" to attract audiences, and protests by animal rights activists over their training and treatment of exotic animals (see below) further cut into their prestige. However, smaller-scale, more theatrical "contemporary circuses" in Europe and acrobatic showcases in Asia were thriving. Canadian company Cirque du Soleil took inspiration, performers, and acrobatic disciplines from such troupes while eschewing animal acts and by the turn of The Nineties managed to revive circus' popularity in North America, providing a springboard for new specialty troupes, as well as a few Follow the Leader knockoffs, to arrive. The competition also probably gave a creative shot in the arm to Ringling Bros., which figured out how to adapt contemporary circus style into its traditional aesthetic and offer an alternative spectacle to those who find Cirque-style shows too "arty".
Minstrel Shows were some of the most popular forms of entertainment in the 19th and early 20th centuries, being viewed as good, clean, light comedy. They were also very culturally significant as one of the first uniquely American forms of artistic expression. As times changed, however, the nasty racial undertones that lay at the core of the genre fundamentally discredited it. Today, it is only used in period works as a way to highlight the Values Dissonance of the era. A notable turning point was in White Christmas, the 1954 remake of sorts of 1942's Holiday Inn. Like Holiday Inn, White Christmas had a minstrel-show number; unlike Holiday Inn, the performers wore tuxedoes, top hats, and gloves, but not black makeup.
Blackface, within minstrel shows and for any other reason, is now extremely taboo in much of the Western world and is used only for historical reasons, irony, or to make a statement about racism. However, this is not the case for some countries that the trope spread to, where it's detached from race relations. One of the most notable examples is Japan, where many people don't understand why it's so offensive and it still has influence on popular culture, leading to many a Cross-Cultural Kerfluffle.
Still, the megamusical's legacy endures. Successful successors to the style emerged in The Nineties with shows that were spectacular but more fanciful and family-friendly — Disney stage musicals, Wicked, Charlie and the Chocolate Factory, etc. And Les Miserables, Phantom, and Miss Saigon still have huge fanbases.
While the concept of the classic Las Vegas showgirl, with her Showgirl Skirt and feathered headdress, remains iconic in the city and depictions of it in pop culture, the actual Vegas showgirl revue is dead. Inspired by European cabaret revues, lavishly-designed shows like Folies Bergere and Lido de Paris ran for decades starting in The Fifties, alternating parades of scantily clad beauties with variety acts. Successors like Splash and Enter the Night simply updated the aesthetics to what was then The Present Day — Goddess, the fictional production in the movie Showgirls, is inspired by those shows.
The format was hit by two different kinds of competition from The Eighties onwards. First, strip clubs lured away guys who came to showgirl revues strictly for the babes. Second, audiences looking for spectacle were captivated by other genres. Stage magicians Siegfried & Roy rose from the ranks of revues to headline Beyond Belief in 1981, and their 1989 self-titled show at the Mirage Hotel and Casino was the show to see in Vegas up until Roy's Career-Ending Injury in 2003. When sister hotel/casino Treasure Island unveiled Cirque du Soleil's Mystere, a show which had spectacle, daring feats, and strong artistic vision (mind-screwy though it was) and characterizations tying it all together in 1993, revues were doomed. As additional Cirque shows and other performance art productions moved into town at the Turn of the Millennium, the "classic Vegas revue" format was recognized as dated, unsexy, and unintentionally campy. Only Jubilee! at Bally's, which opened in 1981, is still running in The New Tens, scraping by on nostalgia for the format and foreign tourists (who may not be aware that it's not an A-list show anymore and/or are on package tours), and in the wake of a disastrously-received We're Still Relevant, Dammit retool in 2014, its days may be numbered.
Touring ice skating revues. Dating back to the 1930s, such shows as Holiday on Ice, Ice Follies and Ice Capades featured glitteringly-costumed ice dancers, stunt skaters, comedy/novelty acts, Olympic champions, and costumed characters from kid-friendly franchises. With a new "edition" each year, they became as much of a family entertainment tradition as touring circuses, but by the end of The SeventiesHoliday on Ice absorbed Ice Follies, and stopped touring the U.S. by the mid-'80s (it still exists in Europe to this day). Ice Capades hung on into The Nineties but fell apart by decade's end, owing to the rise of the extra-kid-friendly rival franchise Disney On Ice and straightforward superstar showcases like Stars on Ice that appealed to serious skating fans — and the skaters themselves. Nowadays the revues are best-known for serving as the real-life basis for the On Ice trope.
Circus and Stage Magician acts involving exotic wild animals (as opposed to often-domesticated varieties such as pigeons, ducks, dogs, cats, horses, etc.) started dying out in The Nineties as complaints from animal rights activists mounted and all-human circuses such as Cirque du Soleil flourished. The onstage mauling of magician Roy Horn (one half of the magic duo Siegfried & Roy) in 2003 by a white tiger effectively killed the use of exotic animals in magic acts. While the best-known "traditional" circus, Ringling Bros. and Barnum & Bailey, still features elephants and tigers in its shows, it's not without controversy.