I am very sorry to hear of your close friend's sad situation.
Frankly, no one can say exactly how long any particular person can survive with End-Stage Liver Disease (ESLD) without having the option of a liver transplant, the only option to continuing living beyond ESLD.
Every person’s liver disease, will to live and situation is unique and must be managed on an individual basis. His medical support team, who is managing his day to day health issues are the only ones who will know his true health status. Which when someone has ESLD, can vary day to day or hourly at the end of life.
Support your friend in whatever way you possibly can. Just being there with them can mean a whole lot when someone is very ill. If you can do that (not everyone can) I think you will help both yourself and your friend.
You may also want to talk with his medical people to get a better idea of his health status and how it will change over time.
My very best wishes to you and your friend.
Hector