I really hope that Hikki is comes back for KH3. That being said, Im actually okay with her not coming back past that. First off, she writes all of her own songs. I dont know if you've ever written a song but that ish is hard. Now imagine doing in it two languages. Plus overachiever that she is, she doesn't write one song and then transliterate it into the other language, she goes and wrote a brand new song for each version (and if you havent read the translations of Hikari and Passion, I suggest you do so immediately). On top of that, KH3 has already been stated to be the culmination of the Dark Seeker Trilogy, so KH4 will be a new take on the franchise. So why not make a fully clean break and have someone like BoA or Angela Aki (both fluent in English) step in for the next three?
On a more serious note, Im wondering what kind of song Hikaru will give us for the last game in the trilogy. I think that KH3 is likely to be the darkest entry in the series thus far, something that Hikaru could probably draw on easily. You see, on August 22nd, 2013 her mother committed suicide after an apparent bout with mental illness. In her first statement afterward, Hikaru stated that she was beyond sad and felt a lot of remorse. In her previous works, her life has somewhat reflected the tone of her music; when she go married her songs were one way, when she got divorced, another. So emotionally, Im curious as to what shed bring to the table for us this time. No doubt that it will be brilliant.