Complex sentence: After doing a search, I can't find any source that says that this "planned" book is existent, so merging into Diary of a Wimpy Kid (series) isn't plausible.
Split into simpler sentences: After doing a search, I can't find any source that says that this "planned" book is existent. Due to the lack of saying that this book even is existent in the planning, merging into Diary of a Wimpy Kid (series) isn't plausible.