I think it's likely he'll go back, but not certain yet.
I believe in rumours that he chose not to choose sides - he'll let the teams solve it out. I think it's plausible, because he likes both places.
Also, I don't think being a starter is a condition for him to move to Madrid (that's how I used to think some time ago), because he's actually a fulltime backup at Juventus now (and that was a big mistake IMO).
Zidane is apparently really into Morata, so if he stays (and chances just went up), Morata is going back.
If he doesn't, there's a chance Madrid will want him only to sell him - that's when we can outbid the profit they'd get.
So, basically it all comes down to Madrid wanting him as a part of the squad. If yes, he'll go back. If not, we have a shot.
Btw, if he moves back there, I feel he'll fail hard. There will be a lot of pressure (also from within - he seems to be too much demanding with himself), and I don't think he'll handle it very well.
So I could actually see him coming back in 2017 for stg like 40M.