I imagine the bookies would take the view that Benitez cannot be the successor to himself :) There would be an almighty row if that happened and the bookies closed the book - unless they laid on him, of course.
Well if that happened, the next Newcastle manager wouldn't be him would it, in which case any bets on the others would ride until Benitez eventually left (or died in-post).
Much more likely it'd be a lift technician.