Some people with COPD (emphysema, chronic bronchitis etc) have high CO2 in their blood, but it seems to be their norm. If they have low O2
levels as well, then they are treated with
oxygen. Prognosis is tough to guess at because people can live with low O2/high CO2 levels for some time if it is chronic. I guess it depends on what is causing the respiratory failure (pneumonia, ARDS, etc would result in acute failure and might be tougher to reverse...).