Final answer:
Edgar Allan Poe's cause of death remains a mystery, but the most plausible theory is that he succumbed to a mysterious illness.
Step-by-step explanation:
Based on the evidence available, the most plausible theory for explaining what happened to Edgar Allan Poe is that he succumbed to a mysterious illness. There is no concrete evidence to support the theories of alcohol poisoning, aliens abduction, or faking his own death. Poe's death remains a mystery, as the exact cause is unknown, but many scholars believe that he may have died from complications related to alcoholism or a combination of factors.