Welcome to the Community,
If the .vmdk data file has been encrypted, then there's no way to use it anymore, like other encrypted files. A new descriptor file won't help, since it basically only described a .vmdk's size geometry, and has nothing to do with the user data.
I'm afraid that the only way to get the VM up and running is to restore the files from the old backup.
recovering the encrypted one is very difficult. If you have a copy of the vmdk file it becomes easier. You have to create a new virtual machine, without HDD. So in the edit settings add a new hdd from an existing file and hook your vmdk. turn on vm and it must work.