what will those in .mil do if/when the money is no good?
Default by .gov at this point is no longer 'if', but 'when...'
Your paycheck, as well as mine, will be worthless.
If it gets bad enough & for those overseas, ie: the sandbox, how wil they get home?
Do the troops ever sit around and discuss these things?
This is actually a subject I've put a lot of thought into.
If economic collapse happened to me while I was in Afghanistan my plan was to walk North to Russia, or Southeast to India. India being by far the easier walk. This was assuming that for some reason the government of the United States just ceased to exist. This was my last ditch, no hope for help from anywhere plan. I gave myself about a 2% odds of success. It wasn't a good plan, but with the assets I had available on my own it was all I had.
However, when a .gov collapses normally the .mil is spared the ravages of collapse for a little while. I think it was in "Starship Troopers" where Soldiers fighting for the US Government were just abandoned overseas after a ceasefire was declared. Somehow the veterans made their way home and took over government....
If a large body of disciplined fighting men were unconstrained in the mayhem that they could unleash upon the steppes of Asia, it wouldn't be the first time. From the Mongols, to the Tar Tars, to the Cossacks, a large number of English speaking professionals would immediately form the biggest, baddest tribe around and start flexing muscle to get home.
My odds of getting home as a member of the biggest baddest tribe to move out of central Asia are much better than me doing it alone. And before anyone wants to bring up the British retreat from Kabul, there aren't too many American Commander's that will not secure the high ground to secure passage through a valley. After all, that is the role of scouts, cavalry, light infantry, and snipers.
Still, I would like to think that the collapse wouldn't be so sudden as to catch everyone with their pants down, especially given how much warning we have.