I'm an Australian, originally here on E3, then H1-B, now green card. I got stuck on just such a trip, to Barcelona. The local US embassy called the wrong number to notify me of my updated passport (which was delivered to a post office only a couple of blocks away, which I wouldn't find out for weeks), and never tried again.

I was stuck for a month, with no possible way of getting back to the US. It's a truly sickening, horrifying feeling, that the only solution is to blow up your life and go back where you came from.

I was extremely lucky that my employers lawyers cajoled them into communication before my money completely ran out.