I dont see Kakashi going crazy if Yamato is killed because honestly Kakashi was closer to Asuma, growing up with him and all, and he kept it cool there letting Shikamaru use his skills, so I doubt he will go crazy if/when Yamato dies. Secondly Yamato is currently stuck in a wall being poisoned on the enemies side, where no one on the JSA knows he is still alive, once things start getting crazy Madara will just kill him and move on to the battle field to end things.