@JorgeB, unfortunately I did not think to take diagnostics prior to rebooting a second time. That was my mistake. @craigr, I did have a backup of the flash drive, so I wasn't hugely worried about losing information or being stuck, I was (and am) frustrated that the upgrades for me have been pretty bumpy. I appreciate all of the work that the team puts into the system, I would like to have a more robust rollback process, ideally automatic, but if manual, "one step" manual versus multiple steps.
That makes me wonder if something akin to timeshift exists - I'll have to look, and if not, see if I can come up with anything, or get those who are sharper than I (a low bar, to be sure) to help create it.