From the people in my company that I’ve asked, they say the rank structure will hold. About 15% disagree, saying they’d refuse orders if they REALLY didn’t want to follow them. I think that the rank structure will dissolve in a friendly way. There is, after all, the argument that the soldiers aren’t getting paid anymore, and their contracts are expiring anyway. Decisions would be made not according to rank, but to general acquiesence + peer pressure.
For punishments, I think the offender would be treated poorly by his fellow soldiers, perhaps given less food or ignored mostly. I’d recommend, however, that the soldiers build a prison out of sticks. Offenders would stand trial and face time in the “fence” under the hot sun w/ little food and water and nothing to do for days. The thought of prison must be worse than any mission that could reasonably be assigned to a person.
When people die, nothing would really change. Kids would be raised under the authority of their parents and upon reaching 13-15 would be subject to group orders. Maybe even the parents could be ordered to tell the kids to do something.