To fix this, simply run:
ecryptfs-rewrap-passphrase /home/.ecryptfs/$USER/.ecryptfs/wrapped-passphrase
It will prompt you for your old passphrase, then allow you to enter a new one. Then, you will be able to log in normally.
Found on: https://askubuntu.com/a/439290/254032
Not sure about recovery options, but as far as getting a usable system, you should be able to reformat the /home partition (since it should be a separate partition, due to the encryption). I haven't really dealt with separate /home partitions much, so not sure what else you'll need to get a usable system. If you have root, you should be ok. If you haven't set a root password (which is generally not recommended, but can be handy if you know what you're doing), I'm not entirely sure how you'd go about getting your user account setup on the fresh /home partition. You may need to research reformatting /home partitions.
The other option is to just reinstall, as you mentioned, and honestly from the sound of it, it won't be that much more painful for you to do it that way, considering you didn't seem to have much going on with your current install.
Oh, by the way, you may want to create a data storage partition. There are two good reasons for this. One, you can have a shared partition that both Windows and Ubuntu can access for media files. Two, if you ever need to wipe one of the OS's out, or get locked out like you have here, the files will still be accessible. Of course, if you want it to be shared, you'll need to make it an NTFS partition, and then setup a UserMap, so that Ubuntu and Windows know which permissions to
As for swap, with that much RAM, you really don't need that much, probably anywhere from 4 to 8 GB should be more than large enough (and I think you can skimp by with as little as 256MB). Swap is important, but you really don't need that much.
Best Answer
I had the exact same problem. I changed my password using
passwd. That messed things up because of the encrypted home directory. The above link contains a solution:login to terminal
You need to know your old password to mount.
Based on grayfox May 17 at 19:28 - http://unixtitan.net/main/2010/11/16/annoyance-changing-password-with-ecryptfs/ (I don't have enough reputation to comment his answer)