If you mean how could they recall them home, Tardises have been shown to have recall devices, as we see the Time Lords summoning the Master in The Five Doctors, and the Doctor in The Trial of a Time Lord.
If you mean how they ressurected the Master, if the War takes place after the TVM from his point of view they may have brought him out of the Eye of Harmony without the Doctor's knowledge, and then gave him an offer he could not refuse.
Well if he was the last, and alone Daleks like to be the supreme force of universe when he made the Daleks, he may have seen it as creating a new Dalek race, separate coped with battle wounds perhaps he discovered some emotions, that hurt him, so he decided to become the god of the new Dalek species, after all he was disfigured after the war, perhaps he never saw himself as a real Dalek anymore.
Originally posted by MrCampion
Well, online news is now claiming the Doctor will not be in the episode that Rose will be appearing in. This seems to confirm Billie is not doing more than just 1 episode as opposed to 3 but if this is accurate (that she and Donna ad Martha team up to save the world) then won't fans feel cheated if the Doctor never comes face to face with Rose?
That was kinda what I was talking about actually.
As for the continuity of the Master- unlikely Jacobi followed Roberts. The Doctor would have recognised him.