Also, it's worth noting that the player-character does not immediately gain any special powers if they do imbibe the ancient magic. Your choice in this scene does not impact your post-game experience and you will still have the same side missions left regardless of what you pick. Sebastian's storyline involving his sister, for example, is not impacted by your choice in the main story. We'll have to wait for a Hogwarts Legacy DLC or sequel to learn more about your character's future!