This happens every once and a while, though it is quite rare in my experience. Usually they are swarms that land on the branch temporarily, only to be trapped on the branch due to poor weather. They give up moving into a new home and begin building combs fully exposed.
I don’t believe there is any hope for the colony exposed like that. Unlike their relatives Apis dorsata (the giant honey bee) http://en.wikipedia.org/wiki/Apis_dorsata, European honey bees don’t do well exposed like that in the cold and rain!
Personally I wouldn’t risk a removal that high. I love honey bees, but I’m not going to risk my life to remove them.
However, if you’re intent on saving them, you’d want to get up there somehow and perform a cutout. You could potentially tie their combs onto some frames/top bars and set them into a hive.