I have huge doubt that Zidane would return to Madrid, at least not when Florentino Perez is still the club's president,
You mean Mourihno, right?
Because, I was talking about Mour.
For Mour's case, his return is very likely. Mour mostly cares about the money, and he has done it before at Chelsea... But he's not the kind of Coach for Real Madrid right now. I feel he will just make things worse with his defensive kind of approach which is not Los Blancos style.
Ronaldo, Di Maria and Ozil who used to catch teams on the break with counter-attacking football are long gone unless there is a complete overhaul in the team.
About Zidane - as long Perez is president of Real, it's impossible that he would return.
And Mourinho - I doubt that he would be best option for Real Madrid.
Even if Real will buy Hazard or another big star, I don't think that it would solve their problems. Most of people think that main reason of terrible Real results is loss of CR7. But I think there is another factor - many of important Real players aren't in their prime anymore like Benzema, Bale. Kroos and Modric also having bad season. I think Real need for rebuild of team to make new "Los Galacticos". But it seems that Perez don't want to open his wallet.