Title says it all. I'm not sure how long I was riding with one of the exhaust bolts gone, but I know it was at least 5 miles. As soon as I realized that was what happened, I took it easy so I could get the bike home. It was just a single exhaust bolt, so the exhaust was still on, just not as secure and I could definitely hear some gases escaping past the headers. On my way to get a replacement bolt now and I'm going to torque the others down again.
I'm wondering why it backed out so much. It can't be but a few rides between when I last tightened them up, but they are coated in anti-seize so I'm wondering if that's just making them back out more than my old ones which didn't have any.
If you replaced the gasket you want to re-torque the bolts a few times after heat cycling everything, or else the bolts will tend to loosen up again. This may be the case with just reinstalling with old gaskets as well, although I'm not sure.
Losing that bolt isn't an issue. Replace it, and you probably should keep tightening them every few days till you find a pattern. I have had a few bikes that loosened those bolts. But most others did not. You may have one of those ones.
Cool.
Buddha.