I liked the episode but I try and forget Myles was supposed to be De Pompedour since the character was paper thin and bland compared to how she comes across in the historical record. A limit to what you can do in 45 minutes though I guess, certainly Moffat never made the historical setting come alive. No problems with the actress coming back as another character though.
I think GITF was the single best episode of Who I've ever seen, with the possible exception of Blink.
Problem is that Sophia played an established historical characters whose death played a major part in the character development of the Tenth Doctor. I don't see her playing the same character - but there is certainly no law against her coming back in another role.
Alex
There was a huge gap before her death that could have been spent with The Doctor - when he found her already dead on his last visit, I thought he may have gone back (again) earlier.
Sadly, can't see the delightful Myles returning though. Anyway, replacing the divine Karen is an impossible task...