It looked like he just took a stage dive into the bushes behind him from my perspective, but I just watched the deleted scene with Michael and Tommasino after the explosion. So, in that way, the novel and the movie are congruent.

As far as Barzini's target actually being Michael, here's a question: what's the percentage in Barzini going after Michael before Vito calls the peace talks? Michael's on ice in Sicily. He's stuck there indefinitely and can't do anything for his family where he is. After Vito calls the peace talks, Barzini would have to know that any action against Michael would be construed by Vito as further treachery and may precipitate full on war.