There's no reason to hang Sai, they're ninjas. If Orochimaru wanted to kill him, the last thing hed do is hang him. I think it is possible that he's dead though since orochimaru said "No matter which way we do it, one corpse is needed now isn't it?" Perhaps Danzou wants Orochimaru to transfer him into a new body? He seems pretty useless in the condition he's in now.