That said, it's refreshing to see new characters, especially a new droid, which vaguely resembles R3PO, but has a winning nastiness and combativeness. So much so, that I grieved at K-2SO's brave death more than for most of the other fierce and savvy rebel fighters who die in battle.
And that was just about everyone, including the blind Chirrut (a nice homage to Marco Polo), who's not blind at all when it comes to the Force, and uses it to better effect than everyone other than D'arth Vader, who of course wields it with awesome power for ill. Vader also of course survives - since Rogue One is a prequel to the first trilogy, and we know when Vader dies, which would be at the end of the third movie in that very trilogy. But just about everyone who's good dies in Rogue One, and that includes especially Jin and Cassian, who had no good reason to die.
Meaning - well, given the odds against the rebels, it makes sense that all of our heroes died, including Jin and K, but that has not stopped our heroes from amply surviving just as deadly and massive and evilly intelligent array of forces in the past (or, the future, if you consider the first trilogy and its one sequel in time).
So why did they all die? I assume to underline the point that Rogue One is a standalone, and we're not going to see any of the characters again, other than Vader and the villainous Tarkin, and maybe a few good rebel Senators. Indeed, so undead is Tarkin that he's played in Rogue One by Peter Cushing, who died in 1994, and had a long career as Van Helsing in the most undead undead series of all time, Dracula.
But the story of Rogue One is not supposed to be about death, but life - or at least, hope - which young Princess Leia, in another reanimated scene, tells us the very end. See this in IMAX 3D if you can - the cinematography is wonderful, stunning, and the story, notwithstanding my quibbles, is a great addition to the canon.
See also: The Force Awakens: Shakespearean and Fun and Ten Reasons to Like the Clones