I'm pretty sure my sim "died" of old age on vacation. It's a very awkward situation now. Since sims don't seem to actually be able to die on vacation, some interesting things happened:
1. ALL family relationships were reset to 0
2. The sim who died was removed from the family tree (and now has a crush on his daughter)
3. The sim who died appeared gray when looking at his family tree (of one...*sigh*) while on vacation, which is how I decided that he had died.
Now that the family is back home from vacation, the old man's color in his family tree is back. He still has a crush on his daughter who he doesn't recognize as his daughter. And we're re-building the relationships. I'm expecting the old man to actually die any day now, but maybe he won't since he already died once.
I run a clean game, and WA is my only EP. (I admit that I did use a cheat to improve the family relationships.) So weird.