More Awesome Than You!

Okay, so I've got this neighborhood with about five families in it, three of which have family ties, and the lot in question is composed of Fergus, his son Franklin, Franklin's wife, Lil, their three kids, Frankie, Farley, and Lana, and two pets, an adopted neighborhood stray dog and a purchased cat. Lana recently grew from child to teen, and I 'forced' Frankie and Farely to grow into Young Adults without a University, as I didn't want to add one (they commute to class, or whatever, thanks to a hack ;D). Lil's pregnant for the first time in-game (the other kids are CAS), and everyone has a job except Fergus who is happily retired.
  Last night I checked in with the Lot, and the splash screen showed the happy family with the most recent clothing changes. Lot loads and it takes me a minute or two until I notice Frankiln's pic is gone. He's nowhere on  the lot, and he's no longer in anyone's relationship listing! In fact, I checked Lil's pregnancy, and the father  is 'Template Sim'! (Checked wants/fears for everyone, just in case they wanted to resurrect him or something, and he had died while I wasn't looking. Nothing.)
  So I got out of the game and opened up SimPE, and there's no memory of Franklin anywhere, including the two other households that contain HIS brothers, or the woman he had a brief affair with! Deleted Sims leave more of a trail!
    Lil's started to notice her Brother-in-law, so I guess things will turn out okay, but that was weird. ???

Sounds like something got borked up when you forced the teens to be YAs without leaving the lot.  It's possible the hack that allows that hasn't been updated for Pets.

I do know that the teens age to YA without going to college hack is NOT compatible with pets. Aging is all messed up with it. I haven't checked to see if there is an updated version, but you can't age to YA with that hack if you have Pets installed. You can age them to adult, but not YA. Your animals won't be able to age at all, and you will have stuck pregnancies with the pets.

I know this from experience. I had to jump through a lot of hoops to get my YAs to live in the main hood. :P

I figured it might be something like that. I don't usually play with aging on, so the hack was 'new'. The kids had been in college for a couple of game plays, so it didn't seem that there were any problems...until the Sim disappeared. I'lll pull the hack and skip the college thing. I can find a workable story for Franklin's disappearance (killed while at work, maybe), but I'd hate to start losing Sims I've grown attached to. Wonder if pulling the hack'll killl the Young Adults?

I'd use SimPE to move them to a house or dorm on campus.  I doubt you can get them there any other way at this point.

I don't know. I couldn't even get my sims to age to YA with that hack in. They'd go straight to adult. Sending them to college turned them into young adults just fine.

I ended up going to a backup I made pre-pets, playing without the hack long enough to get some kittens and puppies, then exited the game and put that hack back in. My YAs MUST live in Pleasantville, lol.

The only thing I would recommend is to avoid moving any existing YAs into the home neighborhood, because they WILL transform into adults.

My way was very roundabout, but I now have my YAs at home, I have a bunch of kittens and puppies (who, of course, will not age :P, but that's fine with me since I also play with aging off), and my game is pretty much the way it was pre-pets, now.

I pulled the hack, and the two college-agers are still leaving for class from home, but the lot's okay, so far as I can tell. (Backing up the neighborhood more often with SimPE, just in case.) Weird, though. First time I'd done a neighborhood with a 'story', and one of the connecting points to all the families disappears. Wonder if the connectiveness was why he was zapped, and not one of the 'forced-aging' teens/YAs?

A friend of mine, who has only base game plus Uni, is interested in this hack.  Where can you get it?