Sahmbi says the android version of Darien will take his place so Darien's superiors in the future would not be suspicious of his possible death and send another retrieval officer. Never mind that Darien's old partner is still in the passed and could identify the android, wouldn't his superiors in the future become deeply suspicious and send another officer (or find his old partner) when it becomes clear Darien is no longer sending anybody back to the future? What's so brilliant about that plan?