If you are a DS female, Carth shows up on the Star Forge and tries to turn you back- there is no option but to kill him. It isn't cut, though, it is in the game; I think you were thinking about the cut ending where you can turn back to the light and die on the Star Forge with Carth.
But as for Dustil, maybe the devs will just assume that if Revan was LS he is alive. If he was DS, you have a dead Dustil. After all, that is probably what happened in most people's games.