Is Erin Hunter going to write any books after the Power of Three?

Yes, Erin Hunter has written books after the Power of Three series. In fact, she has written several more series in the Warriors universe. The series after the Power of Three is called Omen of the Stars, which consists of six books. After Omen of the Stars, Erin Hunter wrote the Dawn of the Clans series, which is a six-book prequel series to the original Warriors series. She also wrote the A Vision of Shadows series, which consists of six books. The newest series in the Warriors universe is The Broken Code, which began in 2019 and is still ongoing. In addition to these series, Erin Hunter has also written several stand-alone novels and novellas set in the Warriors universe.