He left Real because he stopped feeling confident because of management, so he's unlikely to come back, only if management are serious about it and can get him reassured.
Remember that even the first time he did a similar thing, so his return can never be ruled out. After all Real Madrid is sometimes open to the return of their legendary coaches. Let's not forget that it is also Carlo Ancelotti's second spell at the Bernabéu.
I don't know if that's possible now, but why should Anceloti leave? I think the management will do their best to keep him as head coach
At one point he will leave though, probably not in the next couple of seasons, but how knows how the future unfolds.