In the U.S. military, at least, military personnel absolutely do not get “combat pay” (Hazardous Duty Pay) for participating in a war game. You get combat pay for, you know, serving in combat.*
Depending on the details of the exercise and the personnel serving, they would get normal “deployment” pay. As a Reservist, for example, I got Basic Allowance for Housing to help cover my rent while I was on Active Duty. So if I was activated to participate in an exercise, and if the period of activation lasted long enough (I think it must be 30+ days), I’d get that. If the war game lasted long enough (they generally don’t), both reservists and active duty folks would get Family Separation pay. There’s no specific pay bonus for participating in a training exercise, though. That’s just literally part of the job.
Units of sufficient size are usually evaluated, either formally or informally through their chain of command. For example, a Battalion would normally provide at least an informal evaluation of how each of their Companies performed, but that’s not really the point of a war game.
Individuals aren’t normally formally evaluated, though there’s going to be lots of informal evaluation and feedback. In the U.S. Army, anyway, individual performance in major exercises will have an indirect evaluation, as it’s likely to be a bullet point in an NCOER or OER (Non-Commissioned Officer Evaluation Report or Officer Efficiency Report), which are evaluations all NCOs and Officers in the U.S. Army receive on a regular basis. There’s no specific evalution, AFAIK, of anyone’s individual performance in a war game. Again, that’s not really the point.
Anyway, in real life, no one gets promoted for a single exceptional action. There are elaborate bureaucratic procedures managing promotions of NCOs and Officers (for junior enlisted, promotions are more or less automatic as long as you don’t screw up). Demotion only occurs as a punishment for severe infractions that fall short of a court martial, and is pretty rare.
The purpose of war games isn’t actually to win them. It’s to train personnel in realistic conditions, shake out gear, and generally get people involved used to how things actually physically operate in the field. To a lesser extent, they also help planners to test and evaluate doctrines and procedures. And, for international exercises, they are often at least as much about alliance politics and sending messages to potential adversaries as they are about the actual happenings on the ground.
Unless someone really screws up, no one is going to get disciplined for a “poor” performance in a war game. At the National Training Center, the OPFOR (the 11th Armored Cavalry Regiment) was/is infamous for almost always “winning” war games against the units that went there to train. During the Cold War, when it served as a stand-in for Soviet forces, it was only sort of jokingly called the finest Soviet Rifle Regiment in the world.
*Well, not really. You get HDP for serving in a designated Combat Zone, whether or not you personally actually engage in combat.