6. Rose Tyler: Earth Defence
Not a Doctor Who episode but a spin-off, everything was green-lighted for 'Rose Tyler: Earth Defence': she was to follow in the footsteps of Jack Harkness and Sarah Jane Smith, and star in her own show while we waited for her eventual return to the flagship. The show would've revolved around Rose joining parallel Torchwood, just as she claimed she would in 'Doomsday'; an Easter special was planned, reportedly featuring versions of Jack Harkness, Gwen Cooper, Slitheen, dinosaurs and bizarrely Adam Mitchell (you know, that kid from Coronation Street who got a trapdoor in his face in Series 1?) from Pete's World. Russell T Davies apparently cancelled the show though before Billie Piper was even asked, as it was "a spin-off too far", and lessened the impact of her departure. It couldn't have been much worse than Miracle Day though, let's face it.