I was thinking this could be used as a Sabezra or a Kanera idea, so you can do one or the other.
For this I'll just use Sabezra.

Ezra gose on a mission for a long time, leading a group and has to leave the base for a while. The crew think nothing of it but after a month into the mission, they get a call saying that he was in critical condition.

When they got there, they are told that Ezra had (insert any illness), and that he had it for a while. The doctor tells them that he/she thought they knew about his illness but the crew never did.

Sabine then remebered that before Ezra left for his mission, he asked her a question along the lines of "if you were going to die, what would you do?".

Crappy, I know, but it's 5 in the morining.