So sorry, man. Don't know what I'd do if my BGK died. Your fella might have gotten an infection in the wound before you started the melafix; also, they are such loners, he may have been better off in his own hospital tank--less stress the better when ill. Yeah, I say that, but all of mine have ended up as grow-out tanks!
The melafix is really the best all-around treatment unless infection sets in--I've used it many times when my fish have had scrapes or got the cr*p beat out of them (my p. polleni almost destroyed my O; he hung on for a long time but had too much flaying!)