I thought about this a few chapters ago, but this is the first gamble for us readers, where we don't know for sure if Usogui will win. Because in this gamble, from the story perspective, him losing would also work. In fact, if Usogui lost here and died, it would be a pretty good bittersweet ending. As readers, we would be shown that gamble is still a gamble, no matter how good you are, you will run out of luck one day. However, that doesn't mean you should be afraid to gamble, on the contrary, never putting your life on the line in a gamble is essentially not living. We saw this best in character development of Kaji and Hal, who at first were afraid to gamble, Hal even going as far as becoming inhuman, just to avoid gambling. But in the end, no matter how hard they tried to avoid it, to avoid risking, in the end, the only real answer is to not be afraid and risk it all. Both of them learned this through their life, their story. And both of them learned this lesson due to existence of Usogui. So if you look it that way, Usogui's role in the story is now complete.