As I have no experience or expertise with the relevant source materials (such as ancient Hindu and Buddhist texts, languages, and archaeology), I have no answer to give. Until I have a good reason to believe otherwise, I assume the consensus of experts (that he existed) is correct. But how would we know? By testing different hypotheses against the surviving evidence and seeing which one best explains all the evidence we have. It is still possible that even after this we will have an inconclusive result and thus won't know the truth, because the evidence needed to decide the matter has been lost. But in general, does the non-existence of Buddha explain the evidence even as well as a historical Buddha does? You would have to ask an expert in the relevant historical period.
Was Buddha a real person? How do we know?
The Atheist Perspective
How can you dare say that God wouldn't want everyone saved? What about John 3:16? I thought Jesus loved and gave up his life on the cross for the whole world? If not, why create and sustain them? Wouldn't he want them to receive EVERLASTING LIFE?
Do you truly believe, as your god commands, that homosexuals should be stoned to death (Lev 20:13)?
If God doesn't change over time, can He know tensed facts? If not, how is He omniscient?
Answers: Muslim, Christian
How did the religion you adhere to change or develop from its earliest belief form?
Atheist Sense and Goodness Without God: A Defense of Metaphysical Naturalism Richard Carrier Atheist Proving History: Bayes's Theorem and the Quest for the Historical Jesus Richard Carrier Atheist The God Delusion Richard Dawkins Atheist Humanism: A Very Short Introduction Stephen Law Atheist Not the Impossible Faith Richard Carrier Atheist Hitler Homer Bible Christ: The Historical Papers of Richard Carrier 1995-2013 Richard Carrier Atheist Why I Am Not a Christian: Four Conclusive Reasons to Reject the Faith Richard Carrier Atheist God Is Not Great: How Religion Poisons Everything Christopher Hitchens