You can write to the support of coinbase, they'll give you a perfect answer that'll suit your question since everything depends on their willingness to help you recover your funds although it isn't an impossible task since bitcoin and bitcoin cash once operated on the same blockchain as bitcoin cash is a hard fork of bitcoin. I have encountered similar mistakes when I sent ERC20 that's not supported in the exchange ethereum wallet and it got retrieve although I was charged some fees after consulting with the customer care service. Try to contact coinbase support team to get a direct responds.