Markowski is that one NPC that dies in the first level when the Cy-bugs are revealed, to show how powerful and scary they are. That explains his PTSD: at least the others get to kill some bugs first.
…yeah, no-one survives Hero’s Duty. Except maybe Calhoun and Kohut, if you get the Good Ending. Or if you manage to unlock the Easter Egg Ending, where it turns out they were hiding for a surprise party the whole time and the Cy-bugs bake you a cake.