respiratory failure

My husband went into hospital for a knee replacement it did go well. Some time durning the night he experience respiratory failure and was transferred to the ICU and placed on a ventilator. His kidneys shut down and something happened to his liver.He was in ICU for 8days then placed on other floor for rehab. for his knee. He became very slow to talk and many times could not find the words he wanted to say. His thinking is not good to this day he is in a nursing home learning to walk. He has seen every doctor and all the test they have done to find out what is wrong. All the tests were normal. He doesn't even know when to go to the bathroom on his own. It is slow but at times can talk with some sense. The doctors say he choked and caused the respiratory failure. His kidneys have come back now he does not have to be on machine any more. As soon as he can walk on his own I want to bring him home hopeing his mind will come back. He was active healthy 62 year old when he went to hospital now he is a mess. How long will this last or will he never be able to carry on a conversation again. Thank you. MaggieMac