I'm starting to get the feeling that Kaneki doesn't necessarily have to "defeat" Arima to get out of this in one piece. Narukami has broken, Ixa has broken... If Arima's last quinque here were to also break... I can't see him tearing Kaneki apart with his bare hands. But who knows, with Arima? :neutral
I doubt they'd have another quinque ready if Arima's "secret weapon" were to break