I came across an old episode of A Family Affair tonight, and I think it was on TV Land.  Anyhow, Buffy was talking to a new slimmer Mr. French.  A relative told me that "he was the replacement Mr. French while Sebastian Cabot was in the hospital."  Did the slimmer Mr. French permanently replace Cabot after his death, or was it REALLY because Cabot was in the hospital having an operation? 

During the first season Sebastian Cabot came down with pneumonia.  At first it was thought that he just had the flu,  so they had John Williams come in as Niles French under the pretense that Giles French (Cabot) was called to England as a service to the Queen.  Later Cabot's condition worsened and it appeared that he would not be able to continue.   As this point the writers started referring to John Williams' Mr. French as the one and only.  Cabot did recover,  missing nine weeks of shooting and remained in the series until it was canceled in 1971.  Williams' character returned to England.  Sebastian Cabot died at age 59 on August 23 1977,  almost 6 years after Family Affair ended.