Sol's big mistake following on not dissimilar thread

My take, for what it is worth!

Sure thing Turnbull I also "don't think Sonny would have made the deal if Vito had died" especially considering Sonny's blunder, show of greed seemed the 'Go ahead' trigger for Vito's killing [we know different!]

I believe Sollozzo and Barzini would have known “No way was he [Sonny] going to negotiate a deal with Sollozzo” with or without Sonny's greed after Vito's murder

Sollozzo and Barzini were banking on Vito's death, then canvassing the Judges and Politicians who were in Vito's pocket - Vito dead and Barzini offering them a lot more money

If my memory serves me right, Clemenza and Tessio were non-committal when Tom was telling Sonny to make the deal
It undoubtedly would have looked bad for Sonny "if he'd said yes to the deal, he might have been perceived" that Sonny wanted Vito out, to take over