I don't think that Families operating in the shadows of more powerful and bigger Families is the same as being absorbed by those Families or losing all their independence. This has actually been going on historically since the American Mafia's inception. Smaller Families have always acted as a satellite of sorts of bigger Families. I don't think that the Trafficante Family were absorbed, they went extinct, significant difference there. Also, if the Colombos were absorbed by the Gambino Family what would we have? The 4 Families of NYC? You know how boring that would be? Not to mention 4 Families makes it much easier for the feds. I actually remember reading where one agent said part of the problem with NYC vs LCN in other cities is that they have 5 Families to tackle.