Can anyone tell me what dying from empnysema entails?

My husband has COPD (emphysema), on CO2 full time, and has already lived longer than doctors thought. Many people have said the most common cause of death is pneumonia, and he has had two bouts in 15 years, but he's an amazingly healthy guy other than the COPD. It's getting harder for him to breath when he's moving around, but I can't find any straightforward information on what the next years will entail if he stays healthy, but keeps declining. Has anyone been through this?