On a recent evacuation flight by the Royal Dutch Airforce, several nationalities were brought back to Eindhoven from Tripoli, including British, American, French, Belgium and German nationals. They were then "handed over" to their respective embassies for further evacuation and/or accommodation.

I think it's a case by case basis for many countries, at least officially. Most nations probably do not want to be seen planning for the worst: it looks bad to the host nation and possibly creates moral hazard on the part of those who might not otherwise prepare properly (or choose not to travel/live somewhere).

I know the US advertises its citizens are responsible for their own safety while abroad, but they usually (if not always) provide some sort of assistance to US citizens in an emergency. (And often, the State Department sends you a bill afterwards.)