Not necessarily - there's quite a bit that we know was recorded but didn't make the final edit of the movie - full-length Drink With Me, full-length A Little Fall of Rain and the Turning interlude are the ones I know of.
There's been just as much uproar about some of those being cut as there was when Do You Hear the People Sing, A Little Fall of Rain and Who Am I were left off the highlights CD.
Probably only by fans of the show, and the large majority of those buying the album after seeing the film either won't have seen the show, or at least won't be fond enough of it to notice they were missing. I'm all for missing stuff being added to the film score, but if it were a third release it would basically just be fanservice, which I can't see happening. I think anything we don't get on the second album won't be released, there's just not enough left to justify a third one even if an extended cut exists.