Focusing on just the Five Families in NYC, I think at least one of the five will be around in thirty years due to NYC's size, money, and influence in the country. Likely more than one.

I think the best way to gauge the possibility of a collapse of one or all of the Five Families is to look at the collapse of Cosa Nostra Families in other major American cities, say San Francisco and New Orleans. Lack of inducting new members did those organizations in. Smart criminals don't want to become "made" since that puts a bigger target on their backs by the Feds. If the Five Families get weaker then other mafia or organized crime groups could become a more appealing prospect. If a collapse (or collapses) do occur they could unfold relatively quicker than anybody expects.

Do I see signs of an imminent collapse of any of the Five Families, though? No not really, (possibly the Colombo's?)