Most of the cast members still acting today
Except for Ted Knight, most of the major cast members on this show seem to have been blessed with good health and are still relevant 45 years after the show premiered:
Mary Tyler Moore (78)
Gavin McLeod (84)
Valerie Harper (75) was given three months to live almost 2 years ago
Ed Asner (85) still very active with several upcoming roles
Cloris Leachman (89) still very active
Betty White (93) still as popular now as she was back then
Georgia Engle (66)
This is interesting because if you look at shows that aired around the same time like "The Jeffersons" and "Hawaii Five-0" you see that most of the cast members are deceased.