Hello misc, I tried to stop a sysupgrade before it updated anything by pressing the power button, but by the time the computer shut off the install script was already midway through updating the kernel. I know, bad idea on my part.
I was left with an unbootable kernel. To repair it I booted into install72.img, decrypted the disk and copied over the 7.2 kernel from sets. The machine was running -current but I assume the 7.2 kernel would boot it as well. After that however, the bootloader no longer prompts me for the full disk encryption passphrase. Previously it was prompting me for the FDE passphrase before it tried to boot the broken kernel. How to fix this? Help would be much appreciated.