What if Celestia and Luna left Equestria and left Twilight as the ruler of Equestria in season 9's ending, or in the middle of season 9???

[Burning Dusk 46]

I think she will be forced. Because Celestia and Luna does not seem as powerful as they were in the legends. We don't see a lot of their power they were 'Blessed' with. 

Celestia and Luna must have come from somewhere else, they gave peace and now have found someone to replace them. Twilight.

Twilight has found a possible successor that could be Sunset Shimmer as she is being taught the values of friendship like Twilight was. 
Not only that, she seems to have the magical potential also.

[Zestanor 98]

The idea that they came from somewhere else has been around for a while. Faust intended this, and in that one book "Journal of the Two Sisters," it's stated that they were invited to rule from somewhere else, and came as Alicorns. This doesn't make sense anymore, because all of the world has been shown, and there is no Alicorn homeland.

They'll probably 'leave' in the finale. I think they'll remain in the same capacity as Starswirl. They can't very well return to normal society, since they are so powerful. And if what the show says about cutie marks is to be believed, they won't relinquish their day/night powers.

[Burning Dusk 46]

2 hours ago, Zestanor said:

The idea that they came from somewhere else has been around for a while. Faust intended this, and in that one book "Journal of the Two Sisters," it's stated that they were invited to rule from somewhere else, and came as Alicorns. This doesn't make sense anymore, because all of the world has been shown, and there is no Alicorn homeland.

They'll probably 'leave' in the finale. I think they'll remain in the same capacity as Starswirl. They can't very well return to normal society, since they are so powerful. And if what the show says about cutie marks is to be believed, they won't relinquish their day/night powers.

That is very right Zestanor.