Confronting a god of unknown power, origin, and affiliation are probably too much even for Sirzechs. Especially since Rias herself wasn't particularly hurt. And given that just the name "Gremory" had infuriated Ritsuka before he probably wouldn't approach her for negotiations either. Leviathan can do that, but she would probably prefer to watch Ritsuka first and try to figure out who exactly she is. After all, a goddess who had a history with one of the Noble Families couldn't just appear out of thin air, right? And if they figure out that we have angels, fallen angels, and exorcists working for us, things will suddenly become very confusing.
It is also curious that Grigori and Heaven both will be quite interested in Ritsuka - the fallen ones for her ability to modify and enhance them, the angels for the ability to enhance them, as well as the opportunity to give a second chance to the fallen and probably give the chance to become a holy angel to those fallen ones who born, not created by God. It is especially valuable for Heaven, whose number could not increase until recently. Ritsuka is quite capable of bringing the Three Faction War back into the active phase again without even knowing it.
Speaking of factions... I'm very interested in the Khaos Brigade. If Ritsuka wants to leave the world, she may need the help of Ouroboros, and if she can find a way to do so without fighting Great Red, she may suggest that the Infinity Dragon come along. Also, Ophis is her recruiting sempai through the overwhelming force of reluctant minions who don't have her interests at heart. This partnership is a match made in heaven! Or in the Star Sea, rather. It remains only to find a way to find her.