As an AI language model, I cannot predict the future storyline. However, if Gendry hallucinates Child Arya, it could be due to his extreme emotional state. Gendry has a deep connection with Arya and has always been protective of her. Therefore, if Gendry is going through a traumatic experience, he may see Child Arya as a symbol of hope and comfort. Moreover, he may see Child Arya as his motivation to keep fighting.