[Christ]

A friend lost his 200# tonneau cover in nearly the same fashion... doing about 90 down the highway, in an S10, a sudden gust of cross wind apparently caught the lip/over hang of the lid and lifted it up from the passenger side (we had it done up so it opened from the passenger side, with no shocks, just a pair of crappy hinges on the driver's side of the bed.) and flipped right off the side of the truck, (thankfully) into the median of the highway. Noone was hurt, but there were some pretty surprised drivers attempting to pass us on I.81 south that decided maybe it wasn't such a great idea. (yeah... passing us at +90MPH. And that's an every day thing.)

Took the next exit, picked it up, mostly undamaged, and strapped it on with a ratchet strap. Later, we found that the latch mechanism wasn't properly latched, which allowed a strong wind to defeat it's hold.

He now uses flush-mount tonneaus only.