RIP Dawn! I'll always picture you as Mary Ann.
I always preferred Mary Ann! Dawn Wells also seems to have been quite a wonderful person. IIRC, she took care of Natalie Schafer (Mrs. Howell) in the last years of Natalie's life. She remained friends with Alan Hale Jr. (the Skipper) until his death.
Tina Louise (Ginger Grant) always hated being type-cast as Ginger and sought out darker roles that were nothing like the part she played on Gilligan's Island. The last thing I saw her in was the low budget (but really fun!) werewolf flick Late Phases, with a werewolf preying on people in a retirement community on the edge of a wooded area. A blind veteran loses his dog to an attack, realizes what it was, and that he has one month to get ready to kill a werewolf.
So I think Tina Louise is the last of the 7 castaways. It's interesting to read about the show. It was filmed on the studio backlot, near the "prison camp" for Hogan's Heroes, IIRC. I remember hearing that the unheated "lagoon" was always miserably cold, so some shooting days could be tough for the cast members!