To say that God can be killed is wrong. They killed the physical body of Jesus, but He was still God and still very much alive.
To kill the physical body is all that can be done to any of us as well. Physical death however was not the huge punishment that Jesus suffered on our behalf. What he suffered that counts was separation from the Father. This is why Jesus cried out on the cross,"My God ,My God,why have you forsaken me?" This was the first time Jesus had ever been separated from the Father. God wasn't even Father any longer,but "My God".
