I don't see most of the cast changing much as they age anyway.

The Sousanoosenphones or whatever aren't likely to change much except the daughter.

Cotton will eventually die but the rest of the Hills will probably be largely the same.

Dales "son" will change too.

So yeah just the kids.  The only change I see with Hank/Dale/Bill/Boomhauer would be what they hate most at the moment.  Unless Bill eventually gets in trouble for oogling women at the local mall or something.