I speculate that, in some form or fashion, the Time Lords will return at the end. Actually, that's not much of a speculation since a picture of Timothy Dalton dressed in Time Lord robes was leaked months ago.
My speculation is that they have been hiding on Earth with their Fob watches concealing their true identity. I think Wilfred Mott - Donna Noble's grandfather - will turn out to be one of these Time Lords in hiding which will allow to return of Doctor/Donna.
