The disintegration of a complete duplicate of Voyager and its crew, formed from the mimetic Silver Blood of a Demon-class planet, shortly before it could reach the real ship.
In the Voyager episode Demon, a biomimetic fluid on a Class Y planet copies the entire crew. Course: Oblivion picks up the story months later aboard a ship that looks exactly like Voyager, whose crew have forgotten that they are copies and believe they are heading home with an improved warp drive.
Shortly after Tom Paris and B'Elanna Torres marry, the ship and its people begin to break down. Torres dies first. The crew learn the truth: radiation from the new drive is destroying their molecular cohesion, and only their planet of origin could save them.
The duplicate Janeway turns back too late. One by one the senior officers die, the time capsule meant to record their existence is lost, and the ship falls apart just as it comes within range of the real Voyager, which finds only a cloud of debris.