Ideas for the conclusion of Nana by YAZAWA Ai
Things that must be figured out before NANA ends
1. Nana O. disappearance: why it happened, what will happen
2. The relationship between Nana K. and Takumi
3. Nana O. and Nana K. will they be reunited?
4. Shin and Reira is it love?
5. Will Takumi ever change?
6. Yasu, Nobu are these two going to get together with Nana and Hachi, find another girl, or stay alone?
7. Ren? What's up with him? Is he going to find Nana O. and stay with her?
8. The child of Hachi and Takumi
9. The mystery child of Reira???
10. Nana's mother
11. Everything else...
Let's see... this is what I think will happen in my opinion. Considering Ai's other works I do not think it'll be a typical Shoujo ending. Because Ai spent alot of time on this manga hopefully she'll be willing to tie up everything before she ends the series. Rumor has it that Ai mentioned that Nana will end at chapter 77... Thats alot to cover in couple of chapters... Starting from number one: Nana's disappearance most likely something to do with her mother, career going down hill, Ren's cold shoulder towards her when she was in need of help. I do not think she died I think she'll be reunited with Hachi and the rest of the gang- Don't think she'll be a superstar singer though.
The relationship between Hachi and Takumi one of the most complicated yet the most stable relationship so far in the story... I doubt they'll divorce, because they have Satsuki, and some people might call staying together for the child is ignorance but I call that morals (don't argue with me on this one your opinion is yours mine is mine you won't change my mind)

. Personally maybe just hopefully Takumi is going to "reform" or at least try to. For me it will feel like a waste if Takumi and Nana divorces, because I feel that Nana invested alot in the marriage and had to put up with alot and I think if she is going to find happiness through Takumi is the best way for her, because in a way Takumi makes her grow and mature.
Some say they want Hachi to become a single mother and become independent and always whine about how she is not growing mentally. I think she's the one who grew the most in the entire manga. And financially, psychologically being a single mother is alot of strain and loneliness... But at this moment I think Takumi does in fact starts to care about Hachi and does love her in a twisted way. (Takumi and Reira probability of that happening in my book is very very very very low, probablity of the "child" in chapter 70 being Takumi uhhh close the none.)
Shin and Reira, I have no idea on this one. The child of Takumi and Hachi, dude the kid looks exactly like Takumi it's Takumi's, and remember Takumi is the one who made love to Hachi without protection. So the child being Nobu's was slim from the beg. Nana's mother (not a fan of this person) I think this person will deny what she did was wrong till the very end, and refuse to see Nana O. I think its painful but hopefully I am wrong about that.
Sad or happy, this manga is going to have one hell of a ending.