It's probably an oversight. I've completed the game twice already and now I'm testing other options and paths. In a new run I left Rylan in prison until after I defeated Arihama. When I released him, he talked as if he participated in the fight. Then when I went to visit his brother with him, it didn't give me the option to go to Riordan's house after leaving.
Now I'm curious to see what happens if other characters die in the Arihama fight, will test that later.