There is more documented evidence that Jesus did exist, than most personalities of history, that virtually everyone accepts as having lived. These documents are not limited to Christian sources. As such, saying Jesus did not exist would fit in the category of a conspiracy theory on the magnitude of saying the moon landings were really shot in a Hollywood studio. It makes for great fiction, but not history.

But what if Jesus was not the Messiah.

The Messiah was promised by God. God does not lie, so if Jesus was not the Messiah, then all that changes is the timing of the Messiah's coming.

Jesus's teachings would add value to our understanding of what God is asking of His people in the Old Testament in a manner not unlike the Talmud and Mishnah.

I believe Jesus was exactly who He said He was, but if he were not, it really does not change anything. The primary relationship is with God, the Father and Creator. Jesus helped us understand that relationship better, while serving as a sacrifice for the sins of man. If Jesus was a fictional character, it would simply mean the Messiah is yet to come and the New Testament would still serve as a valuable source to understand what God expects of us.