This is a spoiler for KOTOR 1 so a warning is in order
.
.
.
...
.........
The trick is your dialog with Atton in which you determine Revan's Alignment.
If you choose Dark, then Revan works together with a Dark sided Bastila and Carth gets assasinated.
If you choose Light, Revan disappears, but Carth lives an gets promoted to Admiral
After an eternity away from you all, I've returned.