Neither Ume-sensei nor Kirara have actually given any indication of an imminent ending, as far as I'm aware. Still, I would be somewhat surprised if it kept going after Yuno and Miyako's graduation. For one thing, Ume has a lot of other projects on her plate these days. And for another thing, this type of manga rarely fares well when they do try to stick with it into university. Like that's what killed K-On, for example.