A few minutes ago, I rewatched a segment of Doctor Who which featured the departure of the second Romana. I couldn't help but notice that the spaceship in the scene bears a strong resemblance to a certain Firefly-class transport! Clicky
Yeah, it's hardly the first "chicken neck" spaceship in sci-fi. A bunch of stuff in anime comes to mind too. And for some reason, the aerial hunter-killers from Terminator... Mark
He's a robot and a dog, so he obeys his master. Or, like a good soldier, he does his duty. He followed his master's order to protect and serve his mistress. He'd have no reason to want to do anything else.
If memory serves, K9 had somehow become damaged, and could only continue to function in the parallel universe. If he returned "home" with the Doctor, it would likely have been the end of him. Staying with Romana in that other realm was the only solution. Never quite understood how his disintegrating inner works were still working in the other realm, tho'.