Note that I am only referring to the original show, and not the comics which expanded the story.
Through the TV series Buffy The Vampire Slayer and Angel, Cordelia Chase undergoes a massive character growth arc - beginning as a typical snobby, rich prom queen and ultimately
becoming a "higher being".
Season 4 of Angel brings about the extremely controversial pregnancy and relationship with
Angel's son Connor.
This pregnancy coincided with Charisma Carpenter's real-life pregnancy.
After giving birth to Jasmine, Cordelia
falls into a coma and only makes one more appearance in the show during the show's final season.
Wikipedia states (with a citation) that Carpenter's real-life pregnancy required the writers to change much of Season 4's storyline. I have not specifically read whether or not the birth of her own child led her to
effectively leaving the show,
but it would make sense.
Additionally, the writers have said that originally,
the one appearance by Cordelia in Season 5 was meant for Buffy, but had to be re-written due to Sarah's unavailability. It was this episode where Cordelia dies.
Is there any information regarding what the writers originally intended for Cordelia had Charisma Carpenter not become pregnant?