Here's why:
* Mr. D's Role: Mr. D is a significant character in the first book, "The Lightning Thief," but his role diminishes as the series progresses. He's not central to the main plotlines in the later books.
* Sequel Focus: The sequel, "Percy Jackson & the Olympians: The Sea of Monsters," focuses on a different threat and a new set of characters. The story doesn't revolve around Camp Half-Blood or the activities within it, where Mr. D is the main authority figure.
* Character Development: Mr. D's character arc is largely complete in "The Lightning Thief." He doesn't have any unresolved issues or lingering questions that would necessitate his return in the sequel.
While there's always a possibility of surprise appearances in adaptations, based on the source material and the nature of the sequel, it's safe to say Mr. D is unlikely to be featured in "Percy Jackson & the Olympians: The Sea of Monsters."