I'm 74 also and have severe emphysema with a FEV 1 reading of 24 and that's where it's been since my diagnosis nearly 5 years ago. My doc tells me to stay on oxygen 24/7 at 3 setting but..., I've had several problems with that, not the least of which is whether I use the oxygen or not doesn't seem to make a lot of difference 'outwardly' except for the weight of lugging the thing around in a case with a shoulder strap which makes me breathe harder still.
Internally, I realize it's so that my organs have more of a chance of getting the oxygen they need and to that end, I do use the tank for several hours each night while watching television or some other sedentary effort.
The question of "taking care of things" remains for all of us and so is something we all need to attend to when it seems proper and timely to do so. I would think at our age, your husband should realize it's not as "long a road" that is before him as it has been, so he better start cracking !!
As far as how long your husband may have, if that's your central question, I think we're each different and the "final moment" can come at any time regardless of health concerns generally. I think all one can do is "Keep On Truckin' " to the best of one's ability, enjoy the scenery and "take a bit of what is all around you".