Sorry to hear about your crash, but I'm curious how this seat tube failure caused it since you mentioned you were able stand up on the pedals as the seat started giving away. Did the seat jam the rear wheel?

I'm curious because I too sometimes worry about my folders failing, and want to know what to expect. I once forgot to lock the mainframe joint on a folder and hit the ground faster than anything I ever experienced (and I'm a lifelong skier, skater, skateboarder) - very scary. All my other "fall" experience seems to have given me at least a moment to brace for impact.