Well Here It Goes....
After seeing mary killed after the opera .. anthony corleone wants vendetta and no longer wants to be a good boy ...so he joins Vinny and he finishes his law degree and becomes the consingleire... and both control the streets of NYC just like the Ol' Days...
What Do You Think ????
Sorry, but i think it's impossible. One of the Characteristics of The GodFather is that is based on Reality and it never happend. The Family must dessapear as Crime Family, it is what really happend and I think that Godfather IV should pass in these Circumstances.
Sorry for my English, but I'm Spanish