So this happened yesterday. I had ridden to a local shop to pick up something and noticed a tapping noise on the way over. I recognized it from past experience and, sure enough, the chain was tapping the center stand. I had adjusted it not long before, but chains can stretch, etc.
I adjusted it in the parking lot and only made it a couple of miles down the road before I heard something again. Luckily, I was rolling to an intersection that angles across traffic. Not much more than a couple miles an hour. Went to pull out, there was a click/thud....and nothing. For a second, I though I had lost the transmission. "F%@#, this bike's junk now..."
Coasted across the street to the sidewalk and the chain is sitting just as neat as you please on top of the chain guard. Zero damage to me or the bike. Not even a nick or scratch.
I remember when I had the chain off for the rear tire replacement, and I thought then that something looked odd at the master clip. Almost like there were places for two of them, but I only removed one. The master clip was still in the chain. I can only surmise that maybe it had two at one point and one was lost over time?
I got very, very lucky. Installed a new riveted chain today and back on the road!