Now that is an interesting question. As I thought about it, it occurred to me that there are (at least) two different types of betrayal in mob life, each with its own code of punishment:

(1) Breaking omerta, which involves divulging mob confidences to an outsider (a non-mafioso), giving that outsider the power to punish and capture a mobster. In that case, you are betraying not only the mob family to which you belong, but ALL mob families, since you are jeopardizing their livelihood.

(2) Then there's the treachery from the inside, such as what Tessio committed, which involves turning against your own mob family (to side with a rival or to increase your own power).

If Pentangeli killed Michael (or had him killed), then he's a traitor (as in category #2). Michael's people would avenge his murder and exact the punishment of death. Pentangeli would not be allowed to plead or negotiate; and his civilian family would certainly NOT be taken care of . In fact, they may become targets as well, particularly Frankie's brother Vincenzo, since he's already an established mafioso.

However, despite mulling on all that, I realized I'm not any closer to answering Jimmy Buffer's original question. I hope veteran members who are more versed in real-life mafia can chime in and help me. If Frankie breaks omerta, his family is disgraced; other mafia families in Sicily will no longer deal with Vincenzo's organization. I also got the impression from GF2 that these families can also attempt to kill Vincenzo because of Frankie's violation. I wonder if the consequences for Vincenzo would be the same if Frankie's sole crime was to betray Michael à la Tessio (by siding with a rival family and/or attempting to murder Michael). In that case, would other mafia families consider that to be the equivalent of breaking omerta, or would they look on it as an individual mistake on Frankie's part and not let it affect their dealings with Vincenzo?