Hi, My Grandad Is 81, Has Diabetes And Coeliac Amongst

Hi, my grandad is 81, has diabetes and coeliac amongst other health complaints. He's been found to have 3 blocked / failing arteries. He's been told a triple bypass is an option but unlikely due to risk factors in general anaesthetic. They have said stent surgery would be difficult as the arteries are too tightly closed or something? The other option is to control his pain and SOB with medication. Could you estimate how long someone might survive with one functioning artery if they chose only to medicate? (I understand you cannot give a prognosis, I'm just trying to find out if we're looking at weeks, months or years) many thanks, Anna.