User blog comment:B214/Season 3 discussion/@comment-205.217.176.6-20150601045006/@comment-26322543-20150601045339

I don't see why they'd do the RG against Sona, now it'd be pretty pointless.

Think of something similar to the last arc of the Noragami anime. A (not so much in this case) original setting that doesn't interfere with they continuing the story in a possible season 4.