Play on, I say. Random, unexpected occurrences are one of the only things that really keep the game interesting.
Unless you are trying to tell a specific story and need that Sim for the story, then roll back...but it sounds to me like you had autonomy on so I assume that isn't the case.
Chickens can kill Sims, by the way, so maybe that's what happened?
Edit to add: Forgot to mention, you can make sack lunches using left overs of existing group meals that you have on hand. It's much faster (almost instantaneous) than making them from scratch. Just a tip. For a household with 4 school children it's a lifesaver.
I use a mod that puts sack lunches to inventory when they are prepared and just have my school kids pack their own sack lunch from left-overs on their way out the door to school most of the time.