In the comments here is a completely unsubstaniated bit of info that R+V will have a second season. (Warning: Episode 9 spoilers).
After watching episode 8, I considered it highly likely. They are still following the manga, but some of them are filler episodes, with no hint that they are in a hurry to get to the main antagonists shown in the ED. Episode 9, for those of you who have read the manga
Chapters 18 and 19 were rolled together into episode 7, which shorted Mizore a bit. Episode 8 was about Ririko-sensei. If 9 and 10 are a two-parter, then theoretically, that could leave 11-13 for the build-up and showdown with the main antagonists. That’s possible. If Rubi’s plot is a 3 parter, then we’re pretty much assured a second half-season.
Chapters 8, 9, and 10 of the manga involve the “Public Safety Commission” and IMHO, the manga-ka failed to deal with most of the members. It’s going to be hard to pack all three chapters into only two episodes; three is pushing it, especially if they fix his error.
On the other hand, if this is a 26- episode series, the pacing will definitely stagger somewhat, unless the PSC conflict is dragged out through about episode 15. Of course, it could be an odd number like 22, or 24. Well,those are even numbers, but you know what I mean.
One possibility is that they planned for 13 episodes, and the Witch Hill episodes would have been the end. But the series proved popular enough in Japan that they greenlighted the second half after four or five episodes were broadcast; hence the sudden change in OP and ED.
My only major complaint is how cheap the animation looks. They really need to up the budget a bit.