So this is probably one of the most confusing and completely unaddressed factors of the war between Soul Society and Aizen/the Espada. We know they were fighting, we know that Wonderweiss used his ressureccion before reaching Yamamoto, so it could be assumed that he defeated Kensei after transforming, though Kensei's fate is a complete mystery. Overall, nothing is there to tell us what happened. The fight just ended. I assume the above since Kensei never appeared in later fights, though I suppose there could be other reasons for that. Wonderweiss could have just gotten away from him, and he may not have wanted to engage with Aizen and Yamamoto fighting. This answer's basically a big *shrug*, but it's all I've got.
SMH (Sighs) I wish I could tell 당신 what happened but this was one of the things that really upset me about the war arc. I felt cheated since they show his Bankai and then he disappears for the rest of the arc. Right now I assume that he is dead, I say this because (and I hope I'm not spoiling anything for 당신 if 당신 don't read the manga) after the war was over they showed a page where the Vizards were looking down at Hiyori as she recovered (don't know how she lived!) but Kensei and the green haired girl (can't remember her name) were nowhere to be seen. So maybe Wonderweiss killed them. I hope not but it's possible.
Well I read ahead so I just wanna finish it,by saying he lives I don't know how but he does in ch.43something and it shows him still keeping jinta in line.
