You heard that right. The Papa smurf is going to return this march in the last collection of books in the Gathering storm series. The second book "the fracture of Biel-Tan is going to release later this February.
Guilliman's biggest goal is to save the Imperium and supposedly trying to restore it to it's former glory days. Restoring lost technology while cleansing all those who oppose the Imperium in the galaxy. But first he must defend the Ultramar system from falling to the forces of Chaos, particularly the Black Legion.
He has a long and hard task ahead of him, will he succeed or will he ultimately fail? Will he accept the new Imperium or will he drastically change it to how it was? Will he gain overall command over the Imperium? Is he seeking revenge on Fulgrim? Is any other loyalist primarch going to return? All these questions will likely be answered in the final book.