Not the musical theatre that I love. It's not preventing other types of shows from being written or produced. Musical theatre is not vanishing at all. Adaptations of 80s films are no different than adaptations of recent plays and novels were in the 50s and 60s. Tribute musicals and even jukebox musicals have not overrun Broadway or the West End to become a majority or even threaten the existence of any other shows. To believe musical theatre should not exist outside a rigid set of rules and standards is to deny it is an evolving art form like any other. It's like saying Nixon in China is not an opera because it did not follow the form of Puccini or Verdi. Or that the Impressionist or Cubist styles of painting were not art because they were no longer the realistic representations set forth from the previous periods.
If you believe musical theatre is art, then you need to accept that it will evolve, expand and change. And while there is art to musical theatre, like films and music, it is also popular entertainment, and in the case of Broadway and the West End, it is a commercial business as well. Rock of Ages is no more of a threat to musical theatre than Ain't Misbehavin', Smokey Joe's Cafe or Beatlemania. Especially since (at least on Broadway) 80s film adaptations, jukebox musicals and tribute shows have not proven to be historically all that successful. Oustide Jersey Boys and Mamma Mia, Broadway has yet to produce another hit jukebox/tribute musical, though the West End has been quicker to embrace them as evidenced by Buddy and The Rat Pack. And what other 80s film has reached the success of Hairspray other than possibly Fame, but only in the UK and Europe?
If an 80s film adaptation has a score, then it's still a musical. If a tribute show has songs sung by the characters, then it is still a musical. Non-book revues are still musicals. Even unconventional spectacles like Lord of the Rings or Notre Dame de Paris, good or bad, are still musicals. The only shows in recent years I feel have sort of really blurred the line in musical theatre would be Contact or Movin' Out, which are ballets, though Movin' Out does use live music and singers to tell the story.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian