They do not necessarily fly you home if there is a terrorist act in your destination, if your itinerary can skip the one area. Read the small print please!
They do not tell you what to do if the act is before you leave and the US State Dept has not issued a warning yet. Learn the difference between a warning and an advisory and the other vague language used by officials.
So how do you decide if you should go ahead with your trip?
Read and underline the entire State Dept wording. Do not freak at the word warning. Search for the English speaking newspaper of your destination to see what people on the ground are saying. Call some other US based companies and ask if their trips to that destination are still going ahead. Do the same with a few non American companies like Abercrombie Kent .co.uk or Kuoni which is Swiss. Then get hysterical if everyone says Stay Home.