You are correct. Judge Lowell's last appearance was, I believe, in 1978.
We never saw Irma. Her entire relationship with Grandpa Hughes took place off-screen. It was cute, to a degree, but after a while, I think most viewers wanted to "meet" the woman who had captured Grandpa's heart.
No, the funeral was televised. Dr. Bob gave a moving eulogy, explaining that Irma was too grief-stricken to be present that day, and was with her family. I would have been REALLY VEXED if the show had skipped right over the service (the way TPTB did with Mary Matthews on AW, Bert Bauer on TGL, Mattie Lane Grimsley on TEON, etc.) I remember Chris Hughes thanking Nancy for being so kind and loving to his father for so many years, and Nancy replied, "Of course, dear. You see, he was MY FATHER TOO." I lost it and sobbed for several minutes.