As I understand it, there’s a lot more to this story to be told. But the last line of the last episode that I saw sounded an awful lot like “the end”.
Particularly given the subject matter of the show, I’m not opposed to just switching to the light novel, but what do you think?
I do not think the anime will ever continue. Not literally impossible, just highly unlikely. And even if we would get one or two more seasons, there is no way that the anime would ever adapt the whole story. It is just not nearly popular enough and there is a lot of story to adapt. In the end you will still read the books even if the unlikely fourth season happened if you want to finish the story, so why not start now?