(Per Book)The Don liked to say that each man has but one destiny.
But what if he were wrong. What would have changed in the Family if Fredo had been able to successfully defend his father at the fruit stand?

What if instead of mishandling his gun and watching his father get shot, Fredo had been able to shoot or kill at least one of the gunmen and prevent his father from being seriously wounded?

If the Don were still in control, does Sonny go on his roaring rampage of revenge? mad
http://tvtropes.org/pmwiki/pmwiki.php/Main/RoaringRampageOfRevenge

Does the war among the Families still happen?
Does Fredo start to get more respect from everyone?
If Fredo is still around and doing well there's no reason to send him out west..

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.