Obliteration didn't die at the end of firefight, he teleported away. Like most epics he was motivated by his fears, and his lack of knowledge of how to overcome them. His emotional state of mind, which was strongly influenced by the biblical scriptures, lead him to believe that he was one of the four horsemen of the apocalypse, given the destruction his powers could unleash. Like most epics he could not see himself as being a being of evil, so he rationalized his actions by claiming all men, including humans had always had the potential to be epics and therefore were worthy of death. When David revealed to obliteration the truth of his nightmares helping obliteration to realize the means to cure his insanity caused by calamities influenced, he left in search of a means to regain his sanity.