Jesus was unique in that he alone, of all who ever lived, was both God and man. Yes, Jesus Christ could have been God at the moment of his death, as he was fully man and fully God. God can't die. It is also propositional that all humans die. When God came to us in the human flesh, voluntarily laying aside divine attributes in order to humbler himself, his death, as a human was inevitable.
All humans die.
But God does not. Thus it was the human Jesus who died. He could say that, and he did that, because he was fully man and fully God. Hope this helps.