Is it known what happened to the Super Peace Busters after Menma passed away? Did they immediately disband, and immediately stop being friends?
Well, it is no exactly said in the anime but, imagine your best friend just died. Moreover, your best friend just died because of you (they all blamed themselves for what happened). Would you be in the mood to have another get-together? Especially when the get-together is with the same group of friends whom you and your best friend have spent so much time with. It was definitely too painful for each of them. They probably didn't exactly "disband" but just didn't see each other anymore. That's probably why they were still fine with being called the Super Peace Busters and Yukiatsu even calling Jintan "leader". I don't think they stopped being friends either but rather just grew apart. I mean, Yukiatsu and Tsuruko were friends. And Yukiatsu and Anaru were friends. There was a bit of tension between Tsuruko and Anaru (but understandable due to the jealousy and guilt bit and stuff) and Poppo was fine with everybody and Jintan didn't even have the motivation to go to school so it's not really that they hated each other or just stopped being friends. After all, they still probably kept in touch with how Yukiatsu knew that Jintan was registered for the school Anaru joined.