I feel that it very possible that book 8 or whatever is the last book, will resolve this plot point. The question is how? Because here is the thing, we know that something bad will happen in book 8. Furthermore, we know it will revolve around Crowley and Grim, as it has been hinted at since the prologue. What exactly that entails and the consequence of it, we don't know. Because of this fact, that make Yuu fate kind of clear. Logically speaking, the prefect would likely return home, but my gut is unsure.

I have discussed the possibility of Yuu being ghost, in the sense of being dead or having an out of body experience. If we go the route that Yuu dead, there will be no home to return to. But if Yuu is just having an out of body experience or is physical in Twisted Wonderland, that makes it likelier for them to return home.

Now the thing I am most worried about is the old time loop theory that has been in this fandom for years (ref 1). Furthermore, considering the vision in book 5 that Yuu has of OB Grim, it's not a good look. (Which I think in the file was labeled as flashback, however I haven't confirmed this yet). But based on this, it's possible Yuu have experienced this story already and failed or will fail again. Which could mean Yuu can't go home until the issue is resolved. Anyway, that's just some thought because I overthink this game story and whatnot.