I don't see him returning to Real Madrid in their current state, they're clearly not the team they were when he left - and even then they were already starting to decline, their 2017-18 CL triumph was quite lucky if we have to be honest.
And Zidane will leave Real Madrid by the end of this season at the latest, meaning he's without his favorite coach if he should return. Not to forget all the tax dodging others already mentioned.
I gotta see him return before I believe it.