20 Declassified Facts About The Mission: Impossible Series
10. There's An Alan Silvestri Score, Never Officially Released
https://www.youtube.com/watch?v=Ojda6dEmZNYSilvestri was the first composer attached to the first Mission: Impossible film, and De Palma mostly left him alone until the recording sessions. Everything seemed to go well at those sessions, too, at least for the two days they went on, which completed about 19-23 minutes of music for the film.
Then Silvestri got a call from his orchestra contractor. Paramount had cancelled any further sessions. Silvestri shook his head, put the matter behind him and moved on to Eraser. Some fans suggested that he reused most of his M:I work for the latter film, but that seems to be only rumor.
Silvestri was replaced by Danny Elfman, whose work was widely praised, and Elfman was hired to score M:I2... then dismissed as abruptly as Silvestri had been, replaced by Hans Zimmer.