I'm blessed in that I have two children who would take Timber when the time comes. Will they feed him exactly like I do? Probably not. However, I know he is adaptable since I am his third home (at least) and he has bonded to me. Also, he already knows and accepts the kids, which is a good start.
In your situations, I understand it is more difficult. Just my opinion, but where there is life there is hope. While the person who takes your flock members when the time comes may not be ideal, there is no way of knowing if your birds would be "happy" or not, and my initial thought is give them a chance. I'll admit, as Talon implied, I often wonder how satisfying Timber's life is. However, it is all he's ever known. Being hatched in captivity, he's never flown free in the wild or lived a "normal" life. So, I need to believe he is at least content. And, I think he could be content in his next home too.
Have you thought about reaching out to some of the forum members (like SRSeedburners) who are younger and might be willing to take on more flock members? Or maybe your avian vet who may know other younger bird enthusiasts who might be willing? Just a thought.
It's a quandary I know, and like many other things, there is no perfect answer.