If you read the Word you would see that it is God;s Will for all to be healthy, well, healed, and whole. Not once did Jesus "not" heal a person because it was God's Will for that person to be sick, and lame, and dead, and have leprosy. The same goes for your friend, it is "not" God's Will for them to be suffering from liver failure. In Mark 11:23 Jesus told us how to speak to a sickness, He said to tell it what you want it to do.
Here is a prayer you can speak to your friend, while believing in what you are saying.
In the name of Jesus, the liver of Mike is now healthy, well, healed, and whole. I command all liver failure, liver disease, and all works of the devil to leave the body of Mike, now. I declare and I decree Mike shall now be healthy, well, healed, and whole. I bless the body of Mike with the life of God. I cancel all negative words and declarations spoken over the body of Mike. Thank you Jesus.