I imagine the Mirror Universe right now to be Westwood's Red Alert universe. So I would think that there are three possibilities for my counterpart.
1. He's Dead, Jim.
2. He's a low level Soviet Officer.
3. He's a mid level Allied resistance member.
See, the Mirror universe just has to be the opposite of our universe or it wouldnt really be the Mirror Verse. So the USSR wins the cold war. Now where I would fall in, would depend on certain factors, I know that if the Soviets had taken over the US in the 70's, I wouldnt have had the surgery that disqualifies me from military service, so I would have been in the military. But since the Mirror guy has to be my opposite, hes got to be in the Soviet Military. So I wonder how many people my counterpart has killed to maintain the status quo...