So what have we achieved? The source of human error is now on the ground and not first at the scene of the accident caused by his errors. It'll be no cheaper because the "safety critical" workers will now be engineers, flight ops or ATC who will demand higher salaries. All runways will have to be upgraded (see Greek Island thread).
UAVs have advantages because they do not have to be built with life support systems and their cargo is expendable. Doesn't apply to airliners.
There will never be an interim stage where only one pilot is carried "just in case". If you need one, you need two, in case one of them suffers "mechnical failure".
Just my thoughts on it.