Going to ramble a little bit to try to clarify my question a little bit.
I think of the soldiers in Caesars army as the polar opposite of what I’m asking about. They spent massive chunks of their careers in foreign territory, fighting battles, conquering land, and basically just doing war time stuff.
From my understanding, most of a soldiers career would be spent acting as police, laborers and administrators in conquered provinces. Assuming this is even true (which I’m not really sure about) how many soldiers would basically spend their careers doing this kind of stuff versus actually going out on offensive campaigns or fighting huge battles? Would every Roman legionary retire having fought tons of battles? Would the average Roman soldier even see large scale violence in their careers?
We had a nice long discussion a ways back about the likelihood of a Roman legionary surviving to enjoy his retirement.
-- where I wrote a lot, and u/Tiako found exactly the right paper, Walter Schiedel's "Marriage, families, and survival in the Roman imperial army: demographic aspects"
You can follow the link and read at length, but the short answer is: probably about half of soldiers completed their service, and combat death was likely a relatively minor factor compared with accident and disease.