Loser - Zinedine Zidane
The entire profile of Zidane could be tarnished if he takes up this job. He knows it, Florentino Perez knows it and the fans know it as well.
Zidane has the unique distinction of winning a trophy in every season he has managed the club. By taking over Madrid now, he loses that distinction to his name as the club are literally out of all competitions.
Zidane would have been better suited to take over the club in the summer, as he will get a full pre-season to assess his squad and also the possibility of new signings to shape his team in the way he wants.
This would also give him time to find a potential group of players to give him the 40+ goals that Ronaldo guaranteed him every season. Returning to manage Real at this point in this season could tarnish his legacy as a coach.