Conversation so far:
What did John Cleese depart in regards to Monty Python's Flying Cricus?
John Cleese left the Flying Circus at the end of the third.
Why did Monty Python’s Flying Circus end?
Their humor was not always seen as appropriate for BBC, leading to censorship and the remaining Monty Pythons completed a final shortened fourth season before ending the show.
What year did Monty Python’s Flying Circus end?
Monty Python’s Flying Circus premiered on 5 October 1969 on BBC1, with 45 episodes airing over four series from 1969 to 1974.
What other aspects of this article are interesting besides the end of John Cleese's role on Monty Python's Flying Circus and broadcast history?
Monty Python's Flying Circus has become an influential work on comedy as well the ongoing popular culture.

Question: What was the reaction to him leaving?
Self-contained rewrite: What was the reaction to John Cleese leaving Monty Python’s Flying Circus?