I don’t think this will deadlock. To me it seems like a relatively straight forward case; I’m thinking that the reservation(s) will stand as they did before 1907. Poor showing by congress of that time. They forgot to cross their t’s and dot their i’s *and* j’s.
No idea who will write it though.
Roberts, Alito, and Kavanaugh seem to believe it was disestablished; if you examine their comments when it was argued. Thomas was silent as usual, but he generally opposes tribal sovereignty. This makes me think there will be a deadlock. The court tries to spread opinions fairly evenly. Every justice has one opinion from that sitting. I expect a per curiam opinion, which is especially common when cases deadlock or become moot.