Good question British. Let me run down the list.

KC agreed to call it quits. Just a little bookmaking now. Defunct.
LA family was weak even in their peak years, sometimes so weak their rackets were defunct. Pete Milano wasn't afraid to order murders and collect street tax from bookies but for the past decade he was geriatric and now he's dead. Safe to say LA is dead.
Rockford's boss was a hitman for the Chicago Outfit and not really a leader of a family. Only "The Arm" thinks they are viable. Seriously fuck that guy and his legion of misinformation.
Buffalo has plenty of made members but the lack of indictments suggests they're not coming back anytime soon.
Bufalino and Pittsburgh are dead or have one member respectively and were ordered not to open their books YEARS ago.
Rochester had an opportunity when their membership was released from jail, yet they failed to start anything up. That's telling. How do you build something from nothing?

I have often thought about these questions but the fact that a defunct family has yet to be revived shows us that it is unlikely to happen. Can I rule it out? No. Surely there is someone dumb enough to do so but without a network of corrupt police, officials, and muscle they would be easy prey and shut down very quick. That, FBI's successful prosecution for the last few decades, RICO, and changing demographics are why it has not been attempted.

Interestingly, of note, near Pittsburgh there is a town called Penn Hills. A group of non-Italians started a robbery crew which they called the Penn Hills mafia. That's the only "new" family, and their behavior was pretty pathetic. In other words, white kids from the suburbs might go ahead and try it, but building Cosa Nostra out of nothing? Current conditions do not favor it. Not to mention, many of the famous mob families encourage their kids to stay away from the mob and left their children and grandchildren legitimate real estate to save them from the life. So the legacy died with a lot of bosses in the 60's and 70's. So yeah, who is going to continue the legacy?

DeCavalcante's looked to be on the comeback after Frank Guarraci took over. LOTS of new blood. But that new blood was stupid blood. Their capo wanted to whack out a rival with grenade-wielding 1%ers. Its clear that organization has fallen on hard times. I personally don't believe they will make a comeback, but their low-profile members will continue with bookmaking and shylocking. They have about 15-20 years left.

..I personally am in the minority on detroit. I say don't listen to people who say Detroit has made some incredible comeback. There would be a shred of evidence. A bit like Buffalo. They have members but have atrophied.

In reality, Patriarcas have the best hope. They are more active then they are getting credit for.