Below are two clips sent to me by a friend. I personally believe questions about whether reality really exists rank in importance with gods, pleasure, and death. And if we remember that the twelve principles of physics come before the "ethical" conclusions, it is physics is more important.
Does reality exist? What should we think about it? It's not a topic that is omitted from the principal doctrines- it precedes the principal doctrines in development of Epicurean theory, just as the letters to Herodotus and Pythocles precede the letter to Menoeceus. If in fact the universe was created supernaturally, then none of the rest of Epicurean theory makes any sense at all.
And in response to "well maybe reality doesn't really exist - we can't be confident of it because the math and the physics point in all sorts of directions" ---
I think Epicurus confronted exactly the same type of question and fought against it hard -- which we also need to do today.