Arael said: You guys say that every time a new Touhou game comes out. Just give it up man.
That is like telling an addict to stop being one... no, it actually is the same goddamn thing. Anyway, Mima was an awesome character, a playable one to top it, so it is understandable, that people would want her back...
Personally, I have my own reasons for expecting Mima to come back in 13... mainly, there's the whole "Divine Spirits" thing, which the Wiki describes as "A divine spirit (神霊) is the spirit of a human who achieved godhood, either during their life or after their death." Remember that Mima was contemplating becoming a Shinto god. And in addition, there's a rumor going around that ZUN said that he was coding Mima into the game when he got set back due to an HDD failure. Nothing but a rumor, though I'd love if it were true.