In this case, for the manga IS that I began to read. I had read its wikipedia page, so I knew it had been completed quite a while ago. I thought there were only 71 chapters, and 15 volumes. But then, I got confused. I saw an end-of-volume note at around 69 or so. And...it said volume 16 started then. But there wasn't nearly enough material for a 16th volume, and there wasn't an end to the story.
So I checked around, and found that nowhere had those extra chapters that I could find. But, looking at the wikipedia page, I saw that the manga listed 17 volumes. 17, and at 71 chapters, I had only just begun to see volume 16! But then I looked at the date of those releases. The original manga may have finished in 2009...but these scanlations?
Chapter 71 on one site was release on May 18th, 2016. On another, May 17th, 2016. I even found a blog post, written in 2014, that was apparently written by a person working on the current scanlation, which I could tell was accurate because they said "I can't speak for the first 8 volumes, which someone else did, but I have been working on this series since then and I can say it's good", more or less.
Two years ago, just working on the scanlation, with the latest release being back in May of this year. That might seem a bit scarce, but going by the release dates (apparently chapter 70 was released in February, and chapter 69 in December), the manga's scanlation updates at about one chapter per two to three months.
Yes, it's a completed manga, but only in the original language; apparently, in scanlations, it's still very much an ongoing series.
So I'll wait for more. And I do think that more will be released. I was a bit worried, panicked even. I always figured that the story could have a non-ending, ending. But this didn't seem like it. (There's also the worry of it having a depressing ending, but I don't want to find that out for obvious reasons until I read it myself.) I was far more concerned about the possibility that, instead, a far worse thing had happened: the continued scanlation had stopped, and nobody continued after chapter 71.
But seeing those release dates, and their frequency, gives me hope. I'm obviously not gonna know for sure. It's always possible it won't finish. Yet I'll keep on hoping, holding on, to the belief that it's still ongoing, and eventually, I'll be able to read the conclusion of Haru's story, whatever it may be. (Even if it is either a non-ending or a sad ending.)