Until the deuterium runs out
Ya’aburnee cannot sleep without the subtle drone of the caeliomancer. She is the first to wake when it stops. The night crew haven’t even noticed yet when she hails them in a panic.
It is a great honor to be allowed to witness a final transfer. To see a high priest slump over and stop breathing as three miles of starship come alive. Allowed to travel impossible distances. Eternal life in exchange for eternal servitude.
The caeliomancer cannot die or stop or leave. Without it, they are just a metal box floating in intergalactic space.