I noticed that Harriet MacGibbon left "Hillbillies" in 1969, two years before the series was cancelled. Does anyone know why she left? Was she written out or did she quit?

According to Stephen Cox's book THE BEVERLY HILLBILLIES (first published in
1988), Harriet MacGibbon had several health problems. After the series ended,
she did perform in commercials and some small TV cameos but retired in the
1970s for health reasons. She succumbed to a massive heart attack, on Feb. 8,
1987, after a cardiac ailment that affected the last years of her life. Very sad.
(By the way, her favorite role was a far cry from Mrs. Drysdale: it was that of
Mary, the mother of Jesus, in the theater production "The Woman at the Tomb.")

oh, so THAT'S what happened to her! I've always wondered!