Era câncer.
Do Ready Player One (o livro) - Capítulo 1:
Halliday now stands at the front of a funeral parlor, next to an open casket. A second, much older Halliday lies inside the casket, his body emaciated and ravaged by cancer. Shiney quarters cover each of his eyelids.
A razão para o não tratamento é sugerida anteriormente no mesmo capítulo:
Suponho que ele realmente não procurou ou quisesse nenhuma ajuda para o câncer que lhe tirou a vida - ele sabia que ia morrer, e não tinha razão real para continuar vivendo depois de ter trabalhado Ovos de Páscoa no Oasis.He had died a sixty-seven-year-old bachelor, with no living relatives, and by most accounts, without a single friend. He'd spent the last fifteen years of his life in self-imposed isolation, during which time - if the rumors were to be believed - he'd gone completely insane.