This just happened to me a few days ago on a SRAM PC-951 9-speed chain. The chain is about 1000 miles old and hadn't been disassembled for cleanings.

I was out on an easy ride and stopped at a traffic light about an hour into the ride. As I went to continue on when the light turned green, I stepped down and the chain quite literally squirted out the back end of my bike. The quick link had broken (unknown how since I couldn't find it afterwards). I reassembled my chain by breaking it and pushing a pin through (like you would without a quick link) and continued riding. It's been fine so far, but I'll keep an eye on it just in case.