How do you help someone who has end-stage alcoholism?

Love them the best you can. 

If possible, help them get their affairs in order. Estate and funeral planning, etc.

It sounds like it's too late to change the outcome of this disease for them.  They have not been able to make lifestyle changes and are now facing the consequences. Be loving and supportive, without lecturing or nagging. Make the time you have left with them the best it can be.