This morning, the removals were limited to the installed linux-headers packages, including linux-headers-siduction-amd64. I let all the headers go, then reinstalled linux-headers-siduction-amd64, which pulled in the current headers package, and all is good.
On the nvidia driver package update, I did not see the expected warning to reboot or else rmmod nvidia before restarting X. I did the usual procedure to rmmod the nvidia module first, and the GUI came up with no errors.