There are 2 follow ups:
1) Interea - this fleshes out the tour of the wolven moon Amicus and the MC did after Amicus became emperor but before the MC needs to go back to Earth. In Adastra it only got a couple of sentences of mention. This is the currently active story but releases are not as regularly released at times.
2) Khemia - this take place about 2.5 years after the MC returns to Earth. There were only 2 or 3 builds before the author kind of got writers block about how to proceed. He switched to Interea since it's a story he's wanted to do for a while and is using it to help better set the historical background for the Khemia story and some of the characters. This is currently on hiatus, but not abandoned.