I never believed that. Never during the development or in the Kh2 Umltima a woman was said to play a part in Roxas story.
This is a fanfic idea in the making.
1. There is really no need for Namine to go back to the org it take the memories from Roxas. She can take the memories wile not being in physical contact of the person.
2. If she did go back to the org they could easily brake her will to tell them were she been during her disappearance in CO. Thus them capturing Sora and DiZ.
3.Nomura had intentions on having Riku and Roxas meet each other to fight, but it was scratched.
I Days would be about his everyday life with the org and then his recurring dreams as Sora dives him to look for the truth. In the mist of "digging" he finds out Axel and co. been lying to him about the truth in which pushes him to leave. He meets DiZ/Riku telling him to meet Riku at Memory's Skyscraper to tell him about Sora, they fight and KH2 start. I think side plots would be interesting to. Like Mickey and Riku separating, Riku dealing with Ansem inside him, DiZ dealing with Sora's sluber, putting the data in Sora, Axel and Saix over throwing the org, the back stories of the other org members, the secrets of the Org, and due to Coded being strongly tied to what Namine was doing during that time could also be a side plot.