Actually, it's a combination of things as to why Chris left and won't come back. Mainly, he never does sequels or returns back to something after he's done with it. Thus why he suddenly disappeared - pun absolutely intended - into thin air and never showed up again. Contrast to
Eric Roberts The Master, who was killed off in 'Landslide' but proceeded to show up the seventeenth episode of Serieses 3 and 4. As a plus, his character wasn't ruined by actually being the long lost son of Matt Parkman and Nikki who is forced to age backwards thus explaining why he was 10 years older then both of them.
Also, Project: Lazarus, according to wiki, begins a loose trilogy which ends with Evelyn leaving the Doctor. I'm saddened by this, not because Evelyn's leaving but I was planning on listening to them in relatively chronological order instead of release order, and that would include '100', 'Assassin in the Limelight', and the recent trilogy with Brewster. I'll just pretend the next one doesn't start immediately afterward then. :P
Also; re: Doctor Who getting stale. I watch it episodically, with the occasional 'what the hell, two episodes in one night won't kill me'. Exceptions include when there's a movie edit, as I dig that sort of thing. I occasionally have periods where I don't want to watch anything or I'm finding the show a bit tedious, but I usually have something I've been saving that's allegedly good to turn me around. In the case of the last occasion, I had Neverland/Zagreus, which I treated as a five-night event, listening to each one at 9pm sharp. Like Children of Earth.
AIRDATE CONFIRM!
Mark your calendars! Doctor Who returns on August 27th!
Series 6. Part Two! Trailer! Yay!