At the end of the third season, the cast, crew and writers of "Gilligan's Island" expected to return for a forth season. It wasn't just an assumption, they were on the schedule. Over the summer, the head of CBS noticed that his wife's favorite show wasn't on the schedule. To make room for "Gunsmoke", Gilligan got yanked off the air without a farewell, leaving the castaways stranded until they reunited for the TV movie "Rescue From Gilligan's Island" which aired on October 14th 1978.
The movie broke ratings records for TV movies (eleven years after the show ended, viewers still needed closure). If you want to see it, I won't spoil the ending, but I think you can figure it out by the fact there were two more movies to follow: "The Castaways On Gilligan's Island" (Originally Aired 5/3/1979) and "The Harlem Globetrotters On Gilligan's Island" (Originally Aired 5/15/1981)
I wish they would bring it back again
The castaway on Gilligan's Island actually did get finally rescued after fifteen years. They get rescued thanks to Gilligan, but they get stranded back on the island after they go back to their homes, thanks to Gilligan. I saw the movie a few years ago.