This is as difficult as losing the private key to any of your private wallets. It is unfortunate that you will not be able to recover it again, except by chance you are fortunate to have saved it in a place you cannot remember for now and you are later able to find. Another way in which it can be recovered, is if you did not close the account (like it appears on etherdelta "forget account"), you can still withdraw all the coins you have in there.