disclaimer – I’m not a doctor…but the wife is a COPD nurse at the local GP practice(amongst her other roles).
she says its impossible to advise ‘how long is left’ from that one figure, although it’s not a good lung function number as I’m sure you are aware.
she said that it is vital for him to remain free from chest infections especially over the winter. That means being absolutely selfish when it comes to family visits etc and not taking any chances if any of the family have cough/colds etc.
hope this helps a bit, we are having similar issues with a family member 84, COPD, coal fired draughty house and an absolute refusal to accept care/rehousing. quite stressful.