If the system is no longer in ePO, you can recover the key using the DETech tool and the Key Check Value that DETech provides. Once you have the DETech Key Check Value, you can from the System Tree go to Actions > Drive Encryption > Export recovery information based on keycheck (the wording may be slightly different). From that screen, you would input the key check value, and then ePO will give you an XML token that can be used to unlock the drive.
I'd recommend testing this out and see if it would be appropriate for your environment.
Very interesting thanks.
I should have RTFM'd....