I tried reinstalling Daphne and Ports emulators, which did nothing
I wiped the SD card and started over.
After that, I attempted an experiment: with the RPi shiny and new, I changed the resolution with Raspi-Config and rebooted. The EmulationStation never came back. Apparently, in my case, changing the RetroPie resolution is a death sentence. For any reason, you'll never see your ES again.