About a year ago, we pretty much exhausted a thread about Sollozzo's motivation for murdering Vito as a result of Sonny's gaff. In that thread and this one I opined that Sonny's gaff would not convince me that Sonny would approve the deal if I were Sollozzo. I also opined that both Puzo and FFC want us to believe that Sonny's gaff was interpreted by Sollozzo as Sonny's approval of the drug deal. So, that being the case, Sollozzo's getting rid of Vito was logical.

However, without Sonny's gaff, I still think that Sollozzo would have murdered Vito anyway at the behest of Barzini. I figure that Barzini knew that Vito would say no; Vito's No was just a cover. Barzini wanted to be number one. He was already engaged in the drug trade (as was Stracci). Barzini had the resources to sponsor Sollozzo (Vito knew that it was Barzini all along). I figure that Barzini told Sollozzo that once Vito was gone that he and the other families would support Sollozzo's inheritance of the Corleone family. Whether that would eventually happen or not is anybody's guess.