If Jesus is God then how could he die? According to trinitarian theology, Jesus is both 100% man and 100% God. It is said that Jesus, being 100% God, died. Therefore, God died.

I know that 1/3 of God did not die, because that would be tritheism.

So I've considered two other positions:


100% of the living God stopped living. He died and three days later He rose again. 
God did not die in the regular human sense. Just as He is "eternally begotten", He is also "eternally dead". 


Neither of these positions make any sense to me, so perhaps there is a third option. Could somebody please explain how God's death should be understood?
This is where the doctrine of the hypostatic union is essential. Jesus the Son of God is one person, but he has two natures: the divine nature, and a human nature. The two natures cannot be divided, but neither are they mixed in the union to become hybrid natures.

The divine nature cannot die, but the human nature can. Jesus died completely in his human nature. But we do not say that only the humanity of Jesus died - because it is a union in one person we must say that whole person of Jesus Christ, who is the Son of God, died.

Jesus is definitely God, and so there is validity to saying that "God died", but when most people hear that they will understand it as meaning that the divine nature died. I would recommend not to say "God died" and instead say "Jesus Christ the Son of God died".