It isn't "fatalism", quite, as you describe it, "which holds that events are fixed in advance and humans are powerless to change them." It was, at least in my case, more the feeling that I did not want to end up like the so many I watched fry under the pressure. And boy, did they ever. More obstinacy than pride, though there sure was pride too. Most importantly I wanted the respect of those I met with the true grace under pressure.
As far as awareness of death approaching, well, I can see mine coming pretty clearly even if from "natural" causes. My planning horizon does not extend unrealistically now. And it didn't in those old days, either.
Nowadays I conserve my vitality and think about a decade or two, and those days I conserved my vitality and thought about a week or two. Really no difference in anything but quantity.
War is just the same as everyday "peacetime" life, just maybe more so. The pressure exposes differences in character across a spectrum like light through a prism. No hiding, no "carry me" works.
By the way, that is why Liberals are so scared of war. The old timers, like General Patton, knew that sort of person for what he was. A coward.
I personally don't like Scott's Patton. Too much braggadocio, megalomania, grandiosity. Read some of Patton's letters, notable military communication, suchlike. Patton was just a guy trying to get the job done. Aggressive but careful. Not afraid to get his hands dirty.