In Godfather 2 and 3 because of disagreements with Actors or due to unfortunate incidents new characters had to be made these were Frank Pentangeli and Joey Zasa, now my question is if Castellano and Spinelli hadn't died would the story's of their characters have been the same.

In Godfather 2 would Clemenza have been arguing with Michael over the Rosato brothers and have testified against the Corleone family?

Would Willie Cicci have really been so flashy, eager to enter the drug trade and actually betray Michael with the helicopter thing? This scenario seems plausible but Clemenza would be more level headed regarding the Rosato's in my opinion

I don't see any way possible the Clemenza would have testified against Michael, so that arc would have to be changed.

Willie Cicci would have likely testified just as he did. And if so, he wouldn't have been in Zasa's position in 3. Plus he seemed pretty old school, so I would have had a hard time believing he be as out in the open as Zasa.

But how could the Willie Cicci character be still involved in the mafia in the first place after he testified?

Wouldn't he be killed or shunned?

From what I understand, Castellano (Clemenza) would've played the same role as Frankie.

The same applied to Spinelli, who's character Willie Cicci would've played a similar role as Joey Zasa. But the events would've differed a bit.