Motoko will merge with Zero permanently.This will occur some time after Hibiki merges, to no apparent effect. The HiFuMi will then have to take control of her life and start over temporarily merging with Motoko/Zero one by one. When all three have done so, they will then permanently merge with Motoko and Zero, re-unifying Motoko Gettou's psyche.
The final chapter will involve a Gollum style self argument between Gettou and Zero.It has already been shown Zero can talk, and that the personalities are capable of interacting with eachother within Gettou's head.
Zero killed Motoko's mother.It turns out that Zero really was the original personality but had some kind of anger disorder and killed her mother in a fit of fury and developed Motoko as a split personality when she realised what she had done and couldn't handle it. This explains why Motoko only remembers the aftermath of her mother's death.
The conversation in chapter 52 on what would happen if Hifumi and zero went all out for too long will or will almost happen for real at some point.