Comment 48 for bug 358654

I experienced the same issue on Mint 17.1 Cinnamon 64 after a power failure during an update run.
Your methodology of booting a live cd, mounting the partitions, chroot, and complete the updates worked for me and I was able to recover my system.

I posted my experience on the Mint forums here:-
http://forums.linuxmint.com/viewtopic.php?f=46&t=196408