In the first or second issue of New Avengers, Sentry went into space, carrying Carnage (Cletus), and split them/it in half, leaving it to freeze in the vacuum of space.
Flash forward to the mini-series. Some scientists retrieved the Symbiote, and was doing something with it (I can't remember off the top of my head). When it becomes aware, it jumps on the nearest person, which leads them to Cletus, thus rejoining the two. Cletus survived the incident because the Symbiote kept him alive, nearly killing itself.
Also in the mini, the classic Maximum Carnage crew is reunited. Doppelganger, Shriek, and of course, Carnage.