Probably about the 10,000-100,000 bracket, but possibly higher.
That's personally.
In the total war games, I've sacked the planet, defeated the spanish, the french and the american rebels as the british, single handedly, conquered japan, defeated napoleon, scourged europe multiple times, so yeah.
And in star ruler, I've fought in stellar wars that make the culture-idiran war look tame. Especially in the one culminating in the destruction of planets with casual shots.
And destroyed the galaxy, so there's a few trillion lives right there.
If OP would specify if strategy counts, I'll gladly pick a poll choice.