I don't even know what happened, except that I'm not the only one that it's happened to. My game was fine; I sent my heir to France to hopefully find a mate, and when he came back I noticed his elderly mother's portrait was blank and she was frozen (like stuck mid-step standing like a statue frozen) upstairs.
Here's where I made my mistake, I think. Remembering what we did for stuck sims in TS2, I turned on moveobjects and deleted her, then saved, exited, and re-entered the game, expecting to see her at the mailbox. No such luck. Her portrait was still blank and she was still gone.
No matter, thinks I... she was probably ready to die and her death just glitched. I can still play with my heir... and I did... until he went to work, and then ALL the portraits in the houshold disappeared and I couldn't control anyone.
I tried copying my game and using the copy; no luck. I tried extracting the house and household, so I could at least have that in a new 'hood... nope, it crashed the game several times. There's no fixes for the "disappearing UI" problem anywhere that I can find, and they're not even sure what causes it.
It's gone. :(