I'd have to disagree with you on Donna! As long as she's alive, there's always a chance to do something else. They said it was 'impossible' for Rose to come back. So maybe someday, sometime in the future, Donna will be able to come back for a guest episode. And we can see that even without the Doctor, she was able to blossom into this incredible person.

I'm so weirded out by Mickey staying; how about all the things he did in the parallel world? How about JAKE?