Doctor Who: 20 Things You Didn't Know About Heaven Sent
6. It Might Not Have Happened
Can you imagine a world where Heaven Sent didn't exist? Series 9 would be remembered a lot differently, that's for sure.
Clara Oswald was originally meant to die in the series finale, which is in keeping with how Doctor Who has done companion departures in the past. However, Moffat decided that her death would be more impactful if it happened earlier, and so brought it forward to episode ten, which became Face the Raven.
As the events of Heaven Sent follow on from Clara's demise, the episode might not have happened if she'd been offed in the series finale, because, well, that would be the final episode of the series!
Alternatively, Moffat could've written it as a festive special, which would've made Christmas Day 2015 a very depressing affair indeed.