I tried this already. It didn't work.
I am using an undeleted vmx file, though, and if the protection isn't derived from the password, it may be too old to hold the current encryption keys. I decrypted the VM to convert the disk files from sparse to flat format a few months ago and then re-encrypted it. I am not sure if the copy I have is recent enough, however (it should be, can't imagine it would have survived that long). The disk descriptor file was corrupted in the backup and of no use.
I have this problem, because the disk descriptor file somehow went missing from the volume it was stored on and neither undelete nor a backup were helpful in recovering a useful file (throws error: not a virtual disk).
If I just knew how key derivation works, possibly without having to reverse engineer a piece of software as large as a 1GB+ virtualization suite, I could possibly decrypt the virtual disk -- with custom made tools, if necessary -- and create a new VM using it which I could then re-encrypt. But to even assess feasibility and/or what the most convenient approach for recovery would be, I'd really need to know how it works. And details would be nice. 