I don't think it would take a monumental leap for Liverpool or Spurs to overtake us, both teams have had greater spending power than us from 2003 until 2013 (and Liverpool let's not forget finished above us in 2006, 2007, 2009 and last season)....so i repeat to claim that any old manager could have kept us in the top four is for me profoundly flawed.
The point is that the board should be looking within the next six months to make sure someone is in place by the time Wenger contract runs out (Guardiola agreed to take the reigns at Bayern a year before he joined them). If they don't do this than it confirms that we have more to worry about than Wenger.