I've never had handlebars break, but my frame snapped last year, and I've had "what if's" going through my mind from time to time since then. It snapped on the down tube, about a couple of inches from the head tube, so not wildly off the OP. There had been creaking form time to time, but I couldn't find the source, and certainly didn't expect the frame to snap. Anyway, this happened when I was stopping at a red light. The front end just went really spongey and took me a while to figure out what my eyes were looking at. If it'd gone while I was out of the saddle I wouldn't have known anything about it - think the bike would've folded and I'd've been picking up teeth. Like others've said, if your bars are gonna go, it'll most likely be when your putting stress on them. I don't think you'd have time to react.