TV Shows that fell apart once one or more of the cast leaves
I was watching Misfits the other day, and once Robert Sheenan left the show it fell apart and other's started to drop soon after. Nathan was the best character in the show. It wasn't bad after but losing Nathan so early in it's run just took away that piece of the puzzle.
An Australian TV show called The Secret Life of Us, first season was perfection put once a young Joel Edgerton dropped out I think mid way through season 2 and then followed by Claudia Karvan, the show lost the magic it had. By the shows end I think only one original cast member was left.
90's BBC show This Life (known for been the start of Walking Dead's Andrew Lincoln rise) was the perfect show for the Britpop era about a group of 20 something friends sharing a flat. Fantastic soundtrack. With a cast that went on to have good careers. Losing Jason Hughes who played Warren, the young gay lawyer for the start of season 2 was a massive blow (he return for the last episode) but the second season was nowhere near as strong.
Another Andrew Lincoln show this time from Channel 4 called Teachers. The show was very good for it's first two seasons as comedy/drama about the life of Teachers. Once Lincoln and one and two others of the original cast left, it took a massive dip and I don't think in the end it had a original cast member left.