They live forever whether eating or not eating. We all do.
But, in context of 'entering death', yes, they would never enter it if they never ate the fruit.
But, God knew in His wisdom that the fall from grace of a creation with high intelligence, created just beneath the angels and gifted true free will by Him, a good God....be an absolute inevitability. This is why God is completely exempt of evil when He placed the serpent in the garden.
If we parallel humans with angels for example. We find that angels in heaven have eternal life. But they do not have a simple tree of knowledge that determines their path to death over life. Angels fell from grace because as scripture says of the devil in 1 John 3:8 'he has been sinning since the beginning', IE fallen angels are ''sold out to sin''. Sin 'full measure'. Mortal sinners. Unrepentant sinners.
In the case of God's plan for humans. He wanted them to take a different approach to the life and death choice as a result of the creation we are. The purpose for which we were created as seen in multiple scriptures, example in John 1:12-13 Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God. children born not of natural descent, nor of human decision or a husband’s will, but born of God.
A human was created with the intention to be a child of God. This can only happen if from a position of death we choose life and are from this choice birthed into the family of God. Moving from death to life is only possible if there is a worthy sacrifice. Hence Jesus was chosen before the foundations of the earth. Jesus died only for humans. We die to self, a choice of repentance from sin that is on par with martyrdom. We lay our life down for God, God lays His life down for us. An amazing union of a creation with their Creator.
