To be honest, with a broken package manager, the fastest path to a working
system is probably through a fresh install from the ISO (specify the
partition for /home but do not format it!). Of course you want to backup the
user data first... but you have probably already done that, right? If not,
you can do so from the text session with 'cp -a' and an external disk.
You may want as well to save some customized system configuration, in /etc,
and maybe the list of installed packages (to then easily more easily request
their installation, either with 'sudo dpkg --set-selections < file' and 'sudo
apt-get -u dselect-upgrade', or using the menu "File/Read markings..." of the
"Synaptic Package Manager"):
$ sudo dpkg --get-selections > file
