Was the state of Adam and Eve in the Garden the same that we will experience in heaven? We certainly know that they had no sin--it is entirely improper to think of them as being "afraid" of death. Such emotions did not yet exist. So in the sense of not being sinful, they were indeed the same.
Anticipating the Chronicles of Narnia, Augustine tells us that we shouldn't get caught up in what might have happened--we're not told that anyway. Instead, we have to filter our perspective through the lens of God's providence, predestination, and plan:
Our conception of the supernatural City of God must be based on what God foreknew and forewilled, and not on human fancies that could never come true, because it was not in God's plan that they should. Not even by his sin could man change the counsels of God, in the sense of compelling Him to alter what He had once decided. The truth is that, by His omniscience, God could foresee two future realities: how bad man whom God had created good was to become, and how much good God was to make out of this very evil.God does not change His mind--such Scriptural expressions are figurative and there to help us understand God from a human perspective (Calvin would say that God is speaking to us in baby talk, at our level).
Again, this does not mean that God created evil--that comes from man only. Yet, even evil exists only by the permission of God, since it cannot exist without some good to leech off of. In that sense, we don't remove evil "by the destruction of the nature or any part of it." Rather, we need the freedom of the will that comes when man is touched by Divine Grace and restored to a relationship with God. "For that same reason that God's Son is our Savior He is also our Liberator." Liberator from what? From the punishment for our deception by Satan. And it was deception, because the unfallen man could not have directly exercised his will in sin, but had to be led by crooked paths into the action (first Eve, then Adam, and so they share the guilt but not the sin--Milton echoes Augustine in suggesting that Adam sinned so that he would not be separated from Eve).
"To summarize briefly: though not equally deceived by believing the serpent, they [Adam and Eve] equally sinned and were caught and ensnared by the Devil."