How can Rafa gain on clay in 2014? He won everything he played but MC and Novak actually had his worst clay season in years point wise. All Novak has to do different compared to 2013 is to go further than round 1 in Madrid and to not lose in RG before he meets Rafa in the final and that automatically means Rafa can't gain on him in clay points even if Novak fails to defend MC. Everything more than that and Novak will actually gain on Rafa during clay season.
But for the question...AO is crucial, if Novak wins I can see him regaining #1 somehere between IW and Wimbledon, if Rafa wins, it can't happen before USO swing if at all.
You may have a point about clay points, I didn't realize nole may have made less points this clay season, I don't follow his point totals that closely, I was thinking since he won a clay masters, maybe nadal takes that one also.
If djokovic repeats as AO champ again, I think it is likely the #1 spot may change a few times back and fourth this season, if he somehow gets defeated at AO, like you mention, Nadal will likely be #1 most of the Year.