Actually Mormons believe that, since through Adam and Eve’s eating from the tree of knowledge, man gained the freedom of choice in determining his fate. This is pivotal for them since they believe the falling out between Lucifer and Christ during the pre-existence of Earth revolved around Lucifer’s desire to force mankind into salvation and Jesus’s opposing plan to let people decide for themselves.
From a more orthodox point of view, Adam and Eve were already “in Heaven” in the sense of living in the presence of God, while in Eden. Eating from the tree of knowledge destroyed that, and they first hid themselves from God, then were cast out of Eden into a world of sin, suffering, and death. So salvation from sin doesn’t take us to something better than what Adam and Eve had, only restores us to what was lost due to their disobedience.