I’m led to believe it was neither. When Jack was thrown into the future, the timeline was alerted to a future where Aku was never defeated and we got the events of the series, and Jack, being displaced from his proper place in time, stopped aging as a result. When he went back again, the timeline reset to how it would’ve been had Jack been present all along. Of course, this also meant no Aku, and so nobody whose existence depended on Aku’s interference would come to be. The only one who was guaranteed to disappear was Ashi, since she was blood related to him. It’s reasonable to assume that others Jack met in the future would come to be born, just under different circumstances.
As for how long it took Ashi to disappear, I would just chalk that up to a gradual erasure of the potential future timeline that was erased when Jack returned to the past and destroyed Aku.