He fights you anyway as he doesn't need you anymore. The fight is therefore harder as you can't use it to stop his regeneration globe. This guy is obviously untrustworthy so why would you give him a god bow?
Even knowing this I plan to give him the bow anyway, as I can't help but love the character. Also, how could you not make the final battle into VL vs. VL? I'd rather fight darkness with darkness than resort to using a holy artifact. (I'm a PC player and my knowledge is limited, so correct me if it's not possible to fight him in VL form for whatever reason).