The really tragic thing about a show like Who, of course, is that the logistics -- nearly-immortal alien & companion actors who don't want to commit for more than a few years -- mean that the Doctor necessarily has to keep losing people. (The only real solution would be to give him a Time Lord companion, but that is less of an in for the audience, and also even when they tried that Romana ended up leaving him for another universe. Poor Doctor. This is becoming a pattern.) Actually I think the companion who was around longest is probably Fitz, and that's probably because he was only in the novels and no one decided to get rid of him for good.

All this said, perhaps the 2009 episodes, however many there are, will be vignettes of the Doctor and Rose traveling about for a while? Maybe not until she dies of old age/danger/what-have-you, but at least until they've had some more quality time and the Doctor's forgiven himself a bit? I think he's too damaged to be really all right whenever she ends up leaving, but it might at least help.