The 'hard science' approach would doubtless say that if the timeline is changed, that's going to affect everyone conceived within the future light cone of the change. Step out of your TARDIS in 1731, and the ripple effects mean when Mr and Mrs Washington next get busy, a different gamete gets lucky and George Washington has become Mary.
Since that leads to all sorts of uncomfortable fridge logic about whether the time traveller has, by travelling, murdered everyone after the point of divergence, people seem to prefer a softer approach. One such is that people after the divergence behave something like actors; their part may be rewritten, but the actor will still be required on stage at the same approximate time. For example in Kingsley Amis's The Alteration, the timeline diverged from ours in the 16th century but Mozart still turned up on cue a couple of hundred years later. Applying that to the case at hand would mean Zoë would still be around, but she might be working for a biotechnology startup rather than on a space station.
(I've toyed with the idea that it needed the Time Lords to return Zoë to her home timeline, because her visit to the 1960s thoroughly rewrote the 21st century, to the point where the Wheel no longer existed).
no subject
Since that leads to all sorts of uncomfortable fridge logic about whether the time traveller has, by travelling, murdered everyone after the point of divergence, people seem to prefer a softer approach. One such is that people after the divergence behave something like actors; their part may be rewritten, but the actor will still be required on stage at the same approximate time. For example in Kingsley Amis's The Alteration, the timeline diverged from ours in the 16th century but Mozart still turned up on cue a couple of hundred years later. Applying that to the case at hand would mean Zoë would still be around, but she might be working for a biotechnology startup rather than on a space station.
(I've toyed with the idea that it needed the Time Lords to return Zoë to her home timeline, because her visit to the 1960s thoroughly rewrote the 21st century, to the point where the Wheel no longer existed).