Jinton, C4, and Bijuudama are the only things that would be sure kills for him. I'm pretty sure he can survive decapitation, he could just use gathering of snakes to reconnect himself. The only possible ways for him to be killed for good would be Reaper Death Seal (maybe, I'm not sure how that'll play with his curse mark horcruxes), or anything that completely obliterates him leaving behind no DNA.