Sometimes, main/supporting characters will die. Being can’t live forever. Everything has an end. It’s like Han Solo from Star Wars. We have a new story with new people, so Alex’s role became less important. Also, Alex’s death made the next book coming soon become more anticipating.
Alex is dead, there's no going around it. All the magic from Artimé is gone which means the head mage is dead, but honestly I didn't mind his death that much because this series isn't based on Alex, it's based on Thisbe and Fifer and the main focus should be on them, not Alex