Kakashi hadn't recieved Kurama chakra yet so he would have been stuck in that dimension if he had used raikiri. Still, he could have used a kunai or something.
You must be joking. It took BM Naruto, Gai, and Kakashi's combined efforts to break his mask and tear his sleeve and Kakashi could have killed him? Pass on the roofies, man.
No I mean remember when kurama a hurled kakashi at obito, obito sucks him in, kurama attacks and kakashi hits obito from the other side, when obito phased through the attack