Hard to believe, but the BBC weren't sure if Doctor Who could go on without David Tennant. They were seriously considering pulling the plug on the show when the Tenth Doctor moved on, according to head writer Steven Moffat.
Talking to the Hay Literary Festival, Moffat says the BBC were "ready to axe" the show when Tennant and original showrunner Russell T. Davies both left, according to the Radio Times:
I think there were plans maybe to consider ending it. It was Russell T Davies saying, 'You are not allowed to end it' [that kept it going]. David owned that role in a spectacular way, gave it an all-new cheeky sexy performance and became a national treasure. So the idea that Doctor Who could go on at all in the absence of David was a huge question.