Oh poor you, I can only imagine the turmoil you must be feeling, of course you will feel bad if you have to return him, because his chances are somewhat limited at being adopted because of his blindness and now his nature, the thing is he may well be adopted again, but also to a home that does not fit, but you know you can only do your best in this situation, I Know your patience is wearing thin, but please try and give him a few more chances, I really believe a cat therapist is your best bet, they really know their stuff and can offer you advice on how to deal with him.

However having said that, it may not be because Mr Magoo is blind, or has been defending himself out in the wild, it maybe unfortunately just his nature, my own cat Ash is like that, he can be loving and cute and next minute swipe you, he is not a cat to be reckoned with, and I have learn't how to deal with him on his terms, lol, but I know your situation is different, and if he is attacking the other cats, that is a worry.

I really have no experience in this , but just wanted you to know everyone is behind you at PT, whatever decision you come up with , will be supported I am sure, I just wish you all the luck in the world.