So both plants have lost their roots completely. Not sure what did it, but I'm trying to move on!
I've since cut back the damaged portion of each plant (leaving no roots at all), and I've been keeping them in a shallow dish of water with just a whiff of fert in it. I've pulled them out almost daily to give them a few hours of air and to make sure they're not getting too soggy.
Much to my joy, they're both showing signs of roots developing!!! I'm not getting my hopes up, but even the sign of new un-erupted roots is an accomplishment for me. I had to share this excitement!
I wanted to know if this was a "sphag and bag" situation... although to be honest, unless it sounds exactly like what it is, I'm not sure what this encompasses.
Any other suggestions are welcome.