I'm with JC on this one. Although it could be argued that Roth was the prime mover in the Rosatos' attack on Pentangeli, they were still part of the conspiracy. Had they succeeded in killing Pentangeli, and Roth against Michael, the Rosatos would have taken over the olive oil business that belonged to Michael and that was being run by Pentangeli for him. That's more than reason enough.

But, we don't know what happened to the olive oil business after Pentangeli's arrest and the Rosatos' flight. I can't believe Michael simply walked away from it right then. Probably he appointed someone in Pentangeli's stead, and then gradually worked his way out of it. Zasa was in charge of it in 1979, but that was 21 years after the Frankie/Rosatos meeting.