It depends if we count the big 4x strategy games and DEFCON or not. IN FPS games alone, probably more than 100,000 over the years. With < 10k kills in Modern Warfare, Battlefield Bad Company 3, Battlefield 3, etc, I've probably reached 100k on the 360 alone - that doesn't even count the bodies that piled up in games like quake.
If we count 4x games like the total war series, hundreds of millions easily. I often make liberal use of the ideas of total war. For example, in Empire I regularly blitzkreiged across some border, seized some province along with the capital province, burned down every structure in the capital and then gave it back as a peace offering thus allowing me to keep my recent gains without dealing with the rebellions for years all while setting back the foe by years allowing me to focus my forces elsewhere for the time. While few would die in the actual battles, the aftermath certainly killed millions.
If we include Defcon, the numbers are easily in the billions because of that game alone. With Sins of a Solar Empire, it's hard to estimate given the games penchant for numerical abstraction. I assume that reducing worlds to cinders probably carried a staggering price but since the game says the maximum population of a world is "45", it may be that I've only killed a few thousand. Or countless billions.
