I finally got my server back up again. Had upgraded all the virtual machines to FreeBSD 12.1 (from 12.0), and then did the same to the host. When I rebooted the host, the VMs wouldn't boot. I tried installing 12.1 from scratch, in case something went wrong with the upgrade, same thing. Turns out there's a bug
about that. Also, for whatever reason, I didn't take a snapshot before I started, so I couldn't just roll back to before the upgrade. Now I've reinstalled 12.0 on the host and set everything up as it should be again. YAY.
Why didn't I use a turnkey solution like VMWare ESXi? Because "open sores", ZFS, and bhyve sound fancy, that's why.