The thing you need to know about Rogue One, is that yes, there's tragedy, but more than that, it's about hope. It's about people holding on through the most dire of circumstances on the slim chance that there might be hope for the future.

The characters involved die in the hope of achieving a better future for the world around them, and because it leads right into the three original Star Wars movies, we know that said hope proves true, and that they will have been successful in their mission.

It's painful, but the ending is most of all positive, which I feel, now more than ever is essential.