I say try seperating them in different rooms with a window so that they can look at each other. If that doesn't work, the non-deaf cat may feel that the deaf-cat is on its territory, try seperating them. To put deafy out of his or her misery, you may want to put the non-deaf cat for adoption, but if you can't bear to give up a cat, try to give the non-deaf cat to a family member who lives in a different house, that way, you can visit the cat and deafy won't get hurt.