Test Ride not as expected
I was helping a friend look for a KLR 650, and we found one for a good price with not too many miles.
We inspected the bike in the parking lot meetup, and I noted that the chain was nearly new, and had a clip type link that was not safety wired. (You can guess where this is going).
My buddy has taken the safety course but has no experience, so he rode it around the parking lot and turned it over to me for a road test.
I had also mentioned during inspection that the chain was too loose, and would need to be tightened before my friend really rode it (My plan was to adjust the chain after purchase, as we didn't have tools there). Despite that, I took it out on the road because we wanted to see if the transmission got through all the gears and make sure it rolled straight.
As you're expecting, the chain came off at about 50MPH. The tail of the chain smacked up the chain guard really good, and the bike slung the chain down onto the road. Bike stayed upright and I coasted to the side of the road.
I texted my friend 'It runs fine when the chain is on. The chain is no longer on the bike).
We used that to negotiate a better price, and had the guy deliver it. We bought a new rivet type master link, installed it and properly tightened the chain, and were off and running.
Moral of the story: If the chain is too loose, don't ride it. Don't use a clip type master link, but if you must, safety wire it.
Never ride faster than you can stop