So we buy Marota for 22m and Iturbe for 27m. The Vidal sale at the current reported prices don't even cover for these 2 and there's every chance these 2 will fail miserably.
The Zidane example doesn't apply in this era. He was sold for an astronomical price at the time and there were no Mancitys, Chelseas, PSG's, Monaco's, etc. of the world inflating the price of every player who can kick a ball.
If you want to sell Vidal to rebuild, you'll have to sell him for 100m+ to be able to even think about rebuilding the team, and that will only reasonably get you 2 WC players if that.
The smarter thing to do would be to keep the strongest midfielder in the world.