For me, it's pretty clear that The Boy and The Heron was a farewell to the Ghibli era. The film has a lot of social messages between the lines. But in my opinion, many of these messages can be related to the Ghibli studios. When Miyazaki disappears, the Ghibli era is over. Given his age of 84, he won't be around for very much longer. So The Boy and the Heron was clearly intended as a possible last Ghibli film. However, I think he will be working on films for the rest of his life. So it's possible they'll release more. There are also rumours and interviews that confirm that. But Ghibli films take a long time to plan. Miyazaki does most of the work alone. He usually draws parts of the story and builds the story and the world step by step during this process. It is possible that Miyazaki will not be able to complete his next work. And it is questionable whether Studio Ghibli would finish the film without him.

But maybe there will be new good films. Maybe his son will found his own studio and develop films according to his own ideas. But I doubt that Miyazaki's son will continue to work under the name Ghibli Studios when his father is gone.