Who: Lyra Erso, Saw Gerrera, Galen Erso, K-2SO, Chirrut Îmwe, Bodhi Rook, Baze Malbus, Orson Krennic, Cassian Andor, Jyn Erso, and all the rebels Darth Vader easily destroys with his lightsaber.
When: "Rogue One"
Cause of death: Most of them died when the Death Star tested its planet destroyer on Scariff. The point is they all died.
As if the death of Jyn's mother and father weren't enough, and the death of Saw Gerrera early on in the film, the entire cast of good guys and bad guys essentially blows up with the entire planet of Scariff. The deaths of the rebels were expected, but still painful. The less painful death was Orson Krennic, though he was a great character. Essentially, the only characters who survived the movie were Darth Vader and Leia.