My mom has stage iv cancer, so the cancer isn't going anywhere.
My vision isn't exactly the situation you have.
The way I look at it is the following. I really don't look to the future, but plan for now. I try to spend time w/ my mom, keep up w/ daily activities and try find out what is going on in her life. Try to get her involved in things that make her happy. Things that I use to just put off, I take the time and do that now.
I try to get her to look at life differently. Don't be concentrating on what they use to be able to do. Concentrate on making daily life more managable.
Mom can only be active for short periods, gets wore out.
So, lots of repeated things like. Like do things for a short period, take a break. Then when you get your energy back, do some more...
Get them easier tools to prepare meals, friendlier grips, lighter pans, instead of old cast iron, etc.
Encouraging the use of a house keeper on a some basis to help keep the house clean. Having a dirty house because you can't keep it clean because your always tired can be very frustrating, for some people.
You need to find out things that could be extra stress because they aren't as active, and see if there is a soln you can help w/.
Focussing on before is not really positive, for me. You have to make the most of what is going on right now. Else your going to be dwelling on the past. Its fine to remember the good old days...
But as people age, some things get harder to do, being creative and solving problems that cause issues in their daily life could be very helpful.
So, look at their life, see what they love about it, what things frustrate them.
See if there are things that can help w/ what ever frustration they have.
If its physical limits because of the illness, or something like they seem bored, see if there are some new interests or activities which can replace old ones.
Teaching to live your life with flexibility, and also try to roll w/ the punches life gives you a different aspect on life.
I use to spend a lot of time thinking about the moments that my mom would miss, and it wasn't a very pleasant time. Now, I try to think of things that I want to do now w/ mom and do those things. Making more memories now.
So, my advice is to live more in the moment, do what you able to do now, accept what you can do, and move one.