Obviously, Clemenza had a very different personality than Pentangeli,so you couldn't have plunked him down into what GFII became and had it work.

But Clemenza turning on Michael wouldn't have been unbelievable in and of itself. And it would have added a poignancy that Pentangeli's betrayal lacked.

Clemenza was the ultimate loyalist, and a beloved "uncle" to Michael, so him turning would have again showed how Michael lost his family while building his Family.

And it would have foreshadowed Fredo's fate.

"A man in my position cannot afford to be made to look ridiculous!"