We are aware that Chao has return to her own time. We can assumed that something in the future had cause Chao to tried to change the past. It is likely that Chao was sent to the past for some reasons. It seem that she didn't like to be in the past. One of the reasons why she was sent into the past was for her own protection. Chao seem to have come to the past, in order to change it. If Chao went back to the past to change it, the future Mages will have to intervene, in order to stop Chao.
We can conclude that something tragic happen in the future involving Chao and her family. Chao had tried to change the future, but fail as a result of Negi's intervention. What happened is that Chao play her role by shaping the past as it is written in the future. Chao was allowed to return to the future for some reason.
Let's hope that Chao's future is more enlighten. Still, there will continue to be negative events occuring like the tradegy which cause Chao to think about trying to change the future.
I will like to see Chao returning to the past. Chao is a very interesting person. She seems to play a very important role in Negi's life.