TB, my original post was in response to your contention that Buscetta was used by Michael to illustrate to Roth that Michael didn't trust Rocco or Neri. My 2nd post was to illustrate that Michael's use of Buscetta was arranged before the shooting.

Unless I'm misinterpreting the script, after the shooting, Michael tells Anthony that he has to leave early in the morning. Michael is quite capable, but arranging a train trip to Miami and also having Ola there to guide them to Roth is quite a feat apparently arranged within no more than probably an hour of the shooting. So, I conclude that Michael's trip was arranged at least a couple of days before the Communion party and his use of Buscetta was simply FFC's inspiration and was not critically material to the script.

On the other hand, Rocco and Neri were critically material to the script. So, they couldn't be killed in Cuba. Voila! FFC creates a new character (Buscetta) who is expendable.