Harry's exposure to dark matter from the Thinking Cap really takes a toll on his mental capabilities in season four. It's pretty hard to watch his mind slowly regress, especially because he's usually the guy with all the answers. But the silver lining is that he starts listening more to his heart than his head. At the conclusion of season four, he decides to go back to Earth-2 in order to spend more time with high daughter, Jessie. The thought of Harry not being in season five as much is a little sad because a lot of fans really enjoy Tom Cavanagh on the show. But if the writers plan on doing what they did in every other season, Harry will still play a big part in the plot, whether it's Earth-2 Harry or Earth-whatever Harry. Not to mention, we never really got any answers about those strange symbols and scribbles that he was writing on the white board at S.T.A.R. Labs. They match the same symbols that Barry kept writing when he first came out of the speed force and the ones that Nora is seen sketching in her notebook. Surely, these will be explained in season five, which is another sign that Harry's departure isn't permanent.