My solution was eventually to restore the VM from a backup from before the encryption, clone the disk of the encrypted one using Macrium Reflect, and then restore it to the new unencrypted VM.
I never figured out the encryption password, but as long as the login keychain was unlocked it would boot. If it was not, it would ask for a password. The password was not in the keychain, at least not under any name showing up under vmware, fusion or the name of the VM. There is however a fusion encryption key in there, but no password that can be used to decrypt as far as I can tell.
