Personally I'd leave it. If I never existed, then everyone I have influenced may then have never been infuenced. I'm not saying the i'm the most important person in the world, but i'm not worthless either. My existance has so far been worthwhile both for me and for the people around me. To risk disappearing would really fuck things up.
On a smart ass note: Would I be able to "modify" this magic coin before I threw it? If I could, I'd put half a ping pong ball (or equivolent) around the bad half, that way it could never technically land on the disappear side.
I could always just make it a dart and throw it straight up