"Atheists, believes there is no God, thus they know that he does not exist"
No, that is incorrect. Atheists do not claim to 'know' if God does or does not exist. You are confusing atheists with anti-theists. Atheism is a position that the god claims made by religion fail to meet the required standards of evidence to justify belief.
"they mock Him and his believers"
Most atheists I know (and I know many) are respectful of others beliefs when those others are respectful of our beliefs. When we mock believers it is usually when they make demonstrably incorrect claims like the one you are making.
"Skeptics do not know if He exists or not"
Skepticism and atheism are not incompatible. Atheism is a skeptical evaluation of the god claims and the conclusion that they lack sufficient evidence.
"But what if, just what if, at the end, Jesus was real and everything in the Bible was true. What then?"
This is called "Pascal's Wager" and I suggest you look it up before you ask any more questions. You will find the Pascal's Wager is a VERY weak argument for the existence of God. It is popular among uninformed Christians, but avoided by educated Christians and religious scholars because...
(1) The argument isn't specific to any one religion and so can be used to argue for any religion against any other beliefs. Indeed, Pascal was a Catholic and tried to use this to argue for Catholicism against other forms of Christianity. Likewise, a Muslim could use this to argue that Christians should convert.
(2) By this logic you must believe in every religion and every incarnation of god or the supernatural, because any of them COULD be true.