Everyone here in the previous comments are clueless, bitcoin cash and bitcoin use the exact same private keys so if you sent bitcoin cash to a bitcoin address the owner of that bitcoin address can claim it on a bitcoin cash wallet by loading up their private key.
In other words you lose nothing.
What happens depends on whether or not the address was created before or after the split.
Why would it matter if the address was created before or after the split? If it was sent to an address for which someone knows the private key, then they should also have the private key in bitcoin cash.