There is a sequel to Adastra, it's called Khemia which takes place about 2.5 years after the end of Adastra and the first 2 updates are out. But the author was having trouble (writer block) and so put that project on hiatus to do this story first (which he already had mostly planned out anyways).
It looks like he is using this story , Interea, to flesh out and provide background/historical info for Khemia that would otherwise require a lot of flashbacks and such in Khemia. Also it feed everyone desire to see more of Amicus and the MC together.