Ugh! I feel for you, 6 generations and then that happens.
I've got so attached to my sims I've turned aging off for the moment, and I'm aging them up with the cake (They are still at young adult, but I took their eldest up to a child, and forced the triplets to be toddlers - chaos!). I've just found out that I can only force aging once in the PC game, don't know what I'll do!
Why do you want to delete the save game? You could always go back to it later if you think of something else you want to do with it. At the moment I've got several versions of the same two games, to have a kind of 'system restore point' in case one has a problem. The first one I made a mess up and gave the couple a child and two nooboos to begin with in CAS. Because it was the first one I didn't have a clue what I was doing, so decided to start again. This time I started with a couple and saved up a lot of money before they had children so my female sim could quit her job, and the male sim is an astronaut and works one day a week. I want to do more to the house but I'm hitting the horrible fire meter. I wish the developers would take it out.
Some of the lifetime wishes are easy and some are a lot harder. You could try different ways of reaching the same wish. That would be interesting. I want to try a game where the sims reach level 5 in each skill without buying any skill objects as well as working.
I've got Pets but haven't done much with it yet.
One thing I've noticed is that if you hire a babysitter (in the sims 3) while the parents are still at home she hangs around. For days. It's creepy, lol, she never sleeps or eats but watches TV, plays computer games and sometimes looks after the kids. I've found this helpful though since my family has 3 toddlers. Although having said that when I hired the second one she did go after about a day, I'm thinking that the other babysitter hung around because it was the weekend, or maybe it was just a helpful glitch, lol.