I am an atheist. If Jesus returned, as you say, and could prove who he was. Then I suspect most atheists would become his most ardent supporters.
However, I believe it would be extremely difficult for a Christian like yourself. You have many preconceived notions about Christianity, God and Jesus. Some of those notions would have to be wrong and would be the opposite of what you had always believed. (There are numerous Christian faiths with different beliefs. Somebody has to be wrong!) Supposing Jesus said that homosexuality is right with God and you were not to be prejudiced against them, how would many Christians handle that? Supposing Jesus said all atheist were right in not believing in Jesus and that no harm will come to them. Most Christians would go NUTS!
You see, Christian, the return of Jesus would only be wonderful to you IF Jesus is as you claim he is and is not any different from what your teachings believe. But suppose he is substantially different than what you believe? Suppose, just suppose, that Jesus is a Mormon? Will you be so quick to follow him then? I think that eventually, Jesus's biggest enemies would be his former devotees. Always be careful of what you wish for, Christian.
I, on the other hand, would accept him WHOEVER he is.