I love tragic endings too so I think the heartbreaking nature of their story is what especially made this movie stick with me. Although I admit I also love the original idea that Jyn and Cassian would both escape unscathed and the ending of the movie would be their wedding. I think the ending we got was more powerful and moving, but I keep the original ending in the back of my head especially since it seems pretty much every Star Wars couple gets an unhappy ending so I need at least one couple to live happily ever after.