According to Anime News Network (Never liked the reviews they gave) Our beloved TWGOK will also be having ANOTHER OVA featuring Tenri and Diana in all their glory !
So yeah, it will be bundled on Volume 19 obviously featuring Ayumi and Mercury !!
http://www.animenewsnetwork.com/news/2012-07-14/the-world-god-only-knows-manga-gets-new-tenri-anime
Yes people, this is the signal of TWGOk...the signal that season 3 will come !!!