For those who are confused...
Let me just say that I really enjoyed viewing this film and I truely bawled like a baby in my chair, watching this movie. It is sad and also very touching and I enjoyed it very much. The following information that I am about to reveal from here on may contain spoilers for people who have not watched the movie.
From what I read on the IMDb boards on this movie, I realized that there are a few parts about this movie that some people are confused about. And I think one of the confusion was that some people believe that Mio will live the same life, over and over again and never dies. I personally do not think this is true.
The Mio that returns a year after the 28-year-old Mio's death is not a Mio that had died and came back as a 29-year-old Mio with an amnesia, but a 20-year-old Mio that had lost consciousness and jumped forward in time after her car accident. In other words, the body (of Mio) that returned a year after Mio's death is 20 years old. Of course, with no memory.
So what I'm saying is, it is not:
20-year-old Mio(20) -> 28-year-old Mio(28) -> Rainy Season Mio(29) -> Mio, that returns to the past after her realization of her existence(29? 20?)
If it is like above, it would mean that she would live the same life, over and over again. It's quite sad, if you think about it that way. Mio would probably think, "Oh, if I die right now, I'll be born again a year after."
What I believe happened is:
Rainy Season Mio(20) -> Mio, that returns to the past after her realization of her existence(20) -> 20-year-old Mio(20) -> 28-year-old Mio(28)
If it is like I have listed, it would mean there is no Mio after the 28-year-old Mio because Mio dies at the age of 28. So if Mio's spirit was able to see the real world after her death, the 28-year-old Mio's spirit would be able to witness her own 20-year-old presence coming a year after her death to Takumi and Yuuji.
After Mio comes out of the hospital, she comes to a decision from the 6 weeks she spent with her husband and her son (from the time jump), the love she developed again for Takumi, and the desire to give birth and bring her one and only son Yuuji out to the world; therefore, she puts the phrase in her diary: "Right now, I am coming to see you," meaning, she's ready to live the life she already knows what's going to happen (including her early death), just to be with the two people that she loves.
I really hope this was helpful to at least a few people and if there are any other confusion that anyone has, post it here and I'll try my best to answer it. :]