Do cats ever drop dead?

One cat died last winter. She was really sick and skinny and smelly and didn’t eat. It was obvious that she wasn’t going to last much longer.

My other cat is 18. Will we get a warning like with my other cat, or is there any chance she’ll just drop dead of old age? She’s frail, but in fine shape. I’m assuming she’ll at least get smelly; it’d be nice to get some warning to say goodbye.