Just captured him, yay! :D I didn't have the option to fight him (to "wait for Roushk" at the temple) until after I talked to Othra about the lake. I told her to tell the others about it, and then we had the dialogue about capturing Roushk. So now he's in my prison to play with, and the bad lizard tribe ending should happen soon.
Oh, I need to add: I just figured out that the bad ending doesn't happen unless you take him to the temple/lake, even when all the other conditions are met. He was in my prison, and I chose the option from there to take him, and then the bad ending scenes happened. Now, when I go underground at the temple, I have the option to "wait for Roushk" again, so I think I could capture him again, maybe, but I haven't tried yet. Anyway, Rhot hates me now... (;_;) My next MC will have to be very pure to make up for this. haha