Death is not annihilation. Death, as Muslims believe, is experiencing the separation of the spirit and soul from the body. When a person dies they do not cease to exist. So, when we speak of the death of God on the Cross, we are saying that the Divine Son really and truly experienced the end of bodily life. The blood of God was truly poured out on the Cross. Of course, as Luke 23:43 tells us, as soon as God died, He returned to Paradise until the third day. There was never a single moment when the Son did not exist.