Yashiro's death.

I think so ? Since she's not really human anymore.
And she always had a kind of connection with the far shore (even if it's only because she'll die soon)

I think you right, yashiro can become a ghost or spirit.. but i think the story still will go far away, there some chance yashiro not die and still life and there some chance too she will be another supernatural.. it was decided by the event where all supernatural and the number one getting involded *lets just wait the next event ╮(￣▽￣)╭

Who knows, not everyone who dies becomes a ghost. I mean, they become ghosts but their spirits just cross to the far shore, they don't stick around in earth, as they are not meant to do that. From what we have seen so far, doing so is more of a punishment or futile attempts to cling to regrets they can no longer solve.
(I personally wish some people would stop speculating about Yashiro becoming a ghost as if it was a good thing).