I usually keep mine going until there are no more people in the house, even if the parents both die and leave a kid alone. (assuming there is enough food for the kid to eat until he/she goes to college) While I am letting the kid age, I keep looking for collectables, (with more time to concentrate on just that, I have all collectables except 2 of the bugs now) and checking the store, that way, sometimes you can buy magazines or floor repair kits, etc, to have for the next adult, plus maybe new items available in the store by the time they move in. If you buy things your new adult doesn't need, you can always sell them back, except for groceries and upgrades.