I think people were supposed to show up on the planet from time to time without TARDISes being involved. When the episode was going to be where 'The Lodger' is now, they'd have got there by falling through the cracks.

And yes, having seen the full Q&A, what we need is for Gaiman to do as he did with Neverwhere, and novelise his story.

I did chuckle at his reply to the question of whether the Corsair could be cloned or otherwise reconstructed from his arm ala Journey's End:

The Corsair's arm (kidneys, spleen etc) is on a bubble universe that reached Absolute Zero pretty quickly, destroying all the cells, Corsair DNA etc.

Unless of course someone needs it for a future story, in which case it will have been perfectly preserved.