Savino was the key to breaking up the Windows scam, as well bring the initial charges against Chin after he had avoided them for so long. But he certainly didn't take out the entire crew. Same for Cafaro and Fat Tony's crew. Cafaro testified against Fat Tony and gave up a lot of general information about the mob. But his defection wasn't devastating to the crew.

Each rat, especially high ranking ones like Gravano, D'Arco, or Casso, can be very damaging. Not just in terms of their direct testimony but the over all picture they can give to the feds of the inner workings of the families. Who's who. Who has what business. Who's involved in what union. Etc. But the whole point of the mob is that it's not dependent on a single guy. So a crew, much less a family, doesn't crumble because one guy flips or dies.