Stranded in space

I suppose that when astronauts go for space walks, they have a tether or booster packs or some other means of returning safely to the space station/shuttle. But are there any rescue plans in place for the unlikely event that a tether is severed, or a booster pack fails, and the astronaut is unable to return to the airlock himself? Or would such a situation result in certain death for the astronaut in question?

This might help: