People Get the Ending All Wrong
It recently occurred to me that we've all been misinterpreting the ending of this movie.
From Wikipedia: In 1981, the FBI decided to end Pistone's operation. FBI agents visited Ruggiero and Napolitano at a social club and informed them of Brasco's true identity. After the Bonanno leadership learned the truth, they immediately went after the men who brought Brasco into their midst. Mirra and Napolitano were murdered and a contract was put out on Ruggiero. On August 30, 1981, the FBI intercepted Ruggiero as he was going to a meeting at Marangello's social club and placed Ruggiero under protective custody. FBI agent Louis Vernazzo jumped out of a car carrying a shotgun and said, "FBI, freeze!", and arrested Ruggiero on racketeering and gun charges. It's believed that Ruggiero would have been murdered had he attended the meeting.
So when Lefty is sent for at the end of the movie, why does everyone just assume that he is killed? We didn't know the whole story when the movie came out, so maybe we just filled in the blanks and assumed the worst.