The cast learned the show had been cancelled just before the night they would accept their 26th Emmy award. LeVar Burton was the one who made the announcement during the acceptance speech. He could barely mask the rage and the disappointment in his voice.
It ends happily, however, as LeVar Burton pursued and obtained the full rights to the show afterwards and now owns it. It lives on as a constantly updating iPad app that features all of the show's normal contents.
Missing Episode: Two of the shows' 155 episodes were pulled from rotation. They were "Arthur's Eyes" from season 1 in 1983 (because the PBS kids show had that as one of their episodes), and "The Magical School Bus Inside the Earth" from season 8 in 1990 (for the same reason as the Arthur example).