It wouldn't worry me particularly. Frame failure is pretty rare (I've had two break, but that's over many years) and I'd expect that in most cases the best way to deal with it would be to have a replacement shipped out directly or buy a locally available bike to reach a place where one could get a shipment. And if I had to choose between two frames of similar weight but with one steel and the other aluminum I'd certainly put more faith in the aluminum one not to fail in the first place.