It is possible that the intent was not to murder Frankie in the bar. The cop walking into the bar led to total bedlam. When you see Frankie lying on the floor, he is barely alive. He could have been seconds away from dying.
The Rossato brothers were accomplished at killing people, not almost killing people.
The other thing that makes me think that they intended to kill Frankie was that if Roth wanted to turn Frankie into a rat for the feds, sure, it would have taken Michael down, but Frankie probably knew where the other families buried their bodies. Frankie turning state’s evidence would have exposed the other families as well.
I think that the hit was set up to make it look like Michael was behind it to weaken his stake in the New York family.
I just think that when you wrap that piano wire around someone’s neck, it was to affect the ultimate goal. The conversation you reference shows that Michael was not behind the hit. I think that the cop walking into the bar had the unintended consequence of turning Frankie to state’s evidence.
I read somewhere that the actor who tried to garrote Pentangeli was the guy from the Sopranos, who played Paulie Walnuts.