Got them back.
After messing around some more, I realized I wasn't seeing the main viewport in any of the windows. So messed around some more, and came to the conclusion that the main viewport must be stuck somewhere off the screen. This monitor was configured for dual-display (even though I don't have a dual-display- genius), so I reset the monitor to normal display, then the main viewport returned.
However, I then couldn't get the main viewport to live on the main XPression layout, it would fall behind on its own every time I clicked the layout area. I then realized the main viewport had been set to floating. Unchecked that, and then all was back to normal.
Someone really decided to screw with me to start the week. Woof.

#XPression