I ran the command
sudo find / -mtime +100 -delete
The damage was such that when I pressed ENTER on the console it no longer presented a login prompt.
Later on examining the wreckage I found that the process stopped before all files were deleted, and some data could be recovered.
Why?
The findfind command and all of its library dependencies would be loaded into memory before any of its required bits were removed. So why did it stop? Maybe because important files such as /etc/passwd/etc/passwd were deleted?