Can't agree with you on that I think he will stay, unless we are in real relegation trouble, but, it will be purely for financial reasons. Moshiri doesn't want relegation before Bramley-Moore is achieved, he also wants to balance the books. If Benitez can keep us mid table for little outlay, he will be safe.
I really think him being a success is relative, if boring kick and rush football with a badly drilled defence playing deep, who will bypass midfield and hoof it to the forwards 9 out of 10 times, then, he has a chance of success. If however, you want to see some progress made on the playing side Benitez is not, in my opinion the man for you