As a student of international relations I was lucky enough to attend a conference last year in Wellington, New Zealand. This was shortly after the release of the film "Argo" and the guest speaker was Maureen Campbell-White who worked in the New Zealand Embassy in Tehran in 1979.

She said the US acted as something of a lightning rod for all the other diplomats, for whom diplomatic immunity was still upheld. Iran had been something of a tinderbox for a long time previously, so diplomatic missions there always had the threat of possible revolution hanging over them. So they were prepared for possible political uprisings.

She also mentioned how in the film "Argo" they completely ignored the efforts of the New Zealand embassy and New Zealand diplomats in helping the Americans. Not only did they smuggle food to the Americans, but the New Zealand ambassador, Chris Beeby, personally drove four Americans, hidden under blankets in the back of his car, into the New Zealand Embassy compound. Two of which were later delivered to the Canadians.

The reason they didn't close is that when a country becomes politically hostile embassies are supposed to be somewhat like the captain of a sinking ship. They have obligations to their citizens in that country, and to their home government that they can't simply abandon.