Apparently, her final episode is the last episode of this season, which airs in another 3 weeks. Yikes. I wonder what they’re going to do to her. Does she get a happy ending? I’m thinking no — they’ve gone out of their way to play up the relationship between the two of them this season. I think that it can only end tragically.
As far as a new companion goes — here’s my idea: We know that Captain Jack is going to be starring in Torchwood, which airs in the Fall. He’s also got a co-star, Gwen, who is played by Eve Myles, the actress who played the Maid in last year’s episode, The Unquiet Dead.
My guess is that the Doctor will show up at the end of the run of Torchwood (or they’ll devote the Doctor Who 2006 Christmas special to this), at which point, Jack and Gwen become the new companions.