My friend I believe that Jesus Christ would still definitely come to earth even if Adam and Eve did not sinned. It is because of Lucifer. As we all know Lucifer was the son of the morning star, the favorite angel of God, but very ambitious who wanted to be like God. He corrupted several angels and organized his own group, but God stopped all his dirty schemes.
God should have punished outright Lucifer's wrong doings and unrepentant attitude, but instead, sent him to earth together with his followers as their sentence. This is also to show to other angels how good and lenient the kind of God He is. God knew that even on earth Lucifer won't stop his cunning ways. Hence, Jesus Christ still comes because the off springs of the first couple, one way or the other, would eventually be tempted by him leading to commit sins. (Read Isaiah 14:12 to 21)