After Vito was shot, Tom urged Sonny to make a deal with Solozzo. Here's the relevant dialog:

SONNY: Well, Tom -- you're consiglieri, now what do we do if the old man dies, God forbid.
TOM: If we lose the old man we lose our political contacts and half our strength. The other New York Families might wind up supporting Sollozzo just to avoid a long -- destructive war. This is almost 1946 --
-- nobody wants bloodshed anymore. If your father dies, (then) you make the deal, Sonny.

Do you think Sonny would have made the deal if Vito had died?

It's a challenge to believe that Sonny would have overcome his congenital instincts to pursue an intelligent course of action. However, he did do so when he told Sollozzo that he would wait.

The preponderance of advise from Tom, Clemenza, et al would have been to make the deal. They would have pointed out that Sollozzo wasn't going anywhere and he could be dealt with eventually. So, I think that Sonny would have been persuaded to make the deal. However, I don't know how Michael would have reacted.

I think he would have, but constantly try to get Sollozzo afterward. Like he would constantly be operating behind the scenes to try and get revenge while pretending to have forgiven. Which would have caused more issues with the Five Families if he succeeded.

I think Sonny would have made the deal and then killed Sol anyway. If the Barzinis were getting rich off drugs with the Corleones he might have been considered collateral damage not worth going to war for.

I don't think Sonny would have made the deal for several reasons. First, as Oli noted, was his temperament. Second, he realized (per the novel) that when he shot his mouth off at the meeting, he exposed his greed and unintentionally encouraged Sol's attempt on Vito's life. Vito already knew that Tom and Sonny were for the drugs deal. I believe the reason he had Sonny, Tom, Fredo,Tess and Clem present at the meeting was because he wanted everyone to hear that his "no" was final--and wanted Sol to see that everyone heard that final "no" to keep him from trying an end-run around Vito. But, Sonny's outburst became (in Puzo's words), the c***k in the Don's armor." Sonny may have believed that if he'd said yes to the deal, he might have been perceived as benefiting from Vito's death by becoming Don and getting rich from drugs.

Tom's advice was rational, realistic, conciliatory, peaceable--the work of the lawyer that he was. But, he wasn't a Sicilian or a Mafioso. If he were, he would have seen that, if Sonny agreed to the drugs deal, he would have fatally weakened the Corleones by allowing an outsider--not even a made man in the US Mafia--get away with killing the great Vito Corleone. Sonny wouldn't have been the Don that Vito was. But, he was a feared figure in the Mob world, and (again as the novel points out), a superb street general. Fear counts for a lot in the Mob world--that's why Michael never gave anybody a pass, not even his own brother. If Sonny followed Tom's advice, he'd be giving Sol a pass that wouldn't escape notice by the other families, even if he eventually killed Sol.

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

From the novel (the scene where Vito discusses the upcoming Sol meeting with Sonny and Tom):

The Don puffed on his cigar and said, "Santino, what do you think?"

Hagen knew what Sonny would say. Sonny was chafing at being under the Don's thumb. He wanted a big operation of his own. Something like this would be perfect.

My view is that if Tom knew Sonny was "chafing at being under the Don's thumb," then others would know it, too--Sonny being an unsubtle fellow. That's why, if he went for the deal if Vito died, he'd fall under suspicion--not only in the Family but outside, too.

On the other hand, in front of the family's primary protagonists, Tom told Sonny to make the deal.

Yes, but lawyerly advice, not Mafia consigliere advice. Also, since Tom was hot for the deal, not exactly disinterested advice.

Now wait TB. In that scene, Sonny asked Tom for his advice in Tom's capacity as Consigliere. Also, Tom advised Vito to partner with Sollozzo and he gave some very excellent reasons for that advice.

Well Tom you are Consigliere capacity advice

Sonny already said lot of money in that white powder Tom amplified the excellent reasons
make the deal There was no deal Killing Vito was the key
wait If not for Michael, Vito dead

If Sonny had acted on Consigliere Tom's advice, there won't be one place they can hang their hat!

He is a good lawyer not Mafia consigliere

Good points Capri No doubt He is a good lawyer but no Mafia consigliere

I acknowledge this is from the novel...Then, surely Vito would have known it too yet Vito continued to keep Sonny “under the Don's thumb”

Vito was instrumental, contributed, caused the misery of every one of his children, to their gloom and doom indeed

Vito was all business Carmela is the one who kept the family together

He only acted on Sonny's infidelity when his blunder affected business Never mind his wife's feelings of hurt, him cheating on her

True, but there's no indication that Carmela cared about Sonny's infidelity either.

After all, she is the one who told Sonny "don't interfere" when he yelled at Carlo for telling Connie to shut up.

Carmela teased Fredo saying "You don't belong to me You were left on the doorstep by Gypsies”

Poor Fredo copped it from everyone – Vito, Carmela, Sonny, Michael, Greene
No wonder Fredo lapped up all the attention, sympathy and Superman Club visits! from Roth / Ola

True Woltz but when Vito did, it was only when his blunder affected business not because of family values