You think Satter might be alive? The book was published in 1947. Assuming he was 30 in 1947, he'd be 104 now, so... probably not. Of course if this was a Masters or PhD he could have been younger, in his 20's, making him late 90's...We all win when answers are crowd-sourced.
Reading what you've presented so far, I see the lingering question(s) to be "how and why was Tresilian promoted to Captain, and why was his last term of service as a Private?"
If Sattter's book doesn't shed light on this, 1) I think the dude is still alive and 2) data-mine FOLD3 as I suggested above.