I lost a few to damping off - they went flaccid and floppy and a gentle tug revealed them to be rootless. I felt a bit legless myself at that moment. After the horror had subsided, I cut off the roots and sliced back further into healthy looking hypocotyls. I then potted them into vermiculite and they have since started to grow new roots. So maybe I didn't lose them after all. The ones below have escaped intensive care so far.