I Am Power Of Attorney For My Uncle Who Lives

I am power of attorney for my uncle who lives 600 miles away. 3 weeks ago he suffered heart failure his body was filled with fluid. He has been on a triple amount of lasix to rid the fluid. His doctor said he has only 20% of his heart working he is 78 years Los, surgery is not an option. He does have a living will however my question is what time frame am I looking at for his life expectencey he also just completed 3 months of chemo for B cell lymphoma