Oblivion is when someone or something is gone and is long forgotten. "Superman's world was destroyed to oblivion." Being oblivious is when someone is unaware of or has forgotten someone or something else. "Since he was wearing a hat and jacket that day, he was entirely oblivious to the fact that it was raining."

They are related, but not the same, either in use or meaning. 'Oblivious' is an adjective, meaning out of consciousness, not remembered, not noticed. "He was oblivious to (completely unaware of) the fact that his plumbing had sprung a leak." 'Oblivion' is a noun with two meanings. 1) The condition of being unaware, which relates to the adjective's meaning. 2) The condition of being destroyed. "The forest faced oblivion when the logging company bought the land."

one is a noun, and the other is an adjective,