[SPOILERS]Considering that new Minfilia feature.

[EdwinLi]

Ryne was never meant to replace Minfilia but become a separate character that follows her own path in life.

The entire point of Ryne's story is to become a person not "Minfilia" but her own self free of being compared to Minfilia.

It is sad that Minfilia could not be saved but it was expected since she has play little role in the story since her departure in 3.X and it fit her personality that she will not be selfish enough to sacrifice a young girl of her own future just to live when she has tried many times in the past but failed because of their role as the Oracles.

At this point we can basically consider Ryne as Minfilia's daughter( or little sister since Thancred is Ryne's father figure).