It's not that, it's this:
If Real doesn't exercise their option and we sell Morata to anyone else before Real's option expires, then we've to pay Real 80m.
Thats one part of the clause. And you are partly wrong again.
First of all, we CANT sell him to any third club without letting real madrid know, because the clause has a point that says that real madrid can prevent that sale by matching the offer of the third team, but they have 72 hours to bid an offer. If they dont, juve can freely sale morata to the new team.
The other part of the clause says that morata is obliged to accept a return to real madrid if madrid exercise the clause. But If morata refuses to return forcefully, then Juventus needs to pay real madrid 80 million euros as compensantion.
Both pages of the contract in where this clauses appear, are signed by morata himself and marotta. So its GG.