If American Idiot wins best Score it will not only be the death of the Original American Musical, it will be the obliteration of anything sacred in art. Really? All art will immediately cease to exist? This should be interesting. That's giving American Idiot far more credit and power than any Tony award could.
Back in the real world, Broadway is still a commercial venture, so it's not like it holds some sort of invisible responsibility to maintain an impossible level of artistic integrity by those who place unnecessary expectations on it based on a misconception of its history.
American idiot has Neither, since the music came from an album, and the book is based on characters and messages in that album. Just as over 90% of all Broadway musicals have books adapted from one source or another. Legally Blonde and Mamma Mia both had adapted books. One from a novel and a film (Legally Blonde), the other inspired by a film (Buona Sera, Mrs. Campbell). Generally, original books are those not adapted from previously existing material, but written directly for the musical itself. And they have always been extremely rare.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian