In the God of War theme, the last thing the vocals say is "Confront the past". In this DLC, he does just that, therefore he's at peace now. It wouldn't make sense for Kratos to appear in future sequels. Perhaps Atreus will take over as the new God of War? I don't know yet.
This franchise is about Kratos. If there's no more history to tell about him, it must end. I believe there's still a lot to explore, especially after that "therapy" in Valhalla. We saw young Kratos being a monster, older Kratos trying to be better, and now it's time to see older and wiser Kratos being the best he can be.
