You have to ask why Renault passed on him and put Ocon in the car...
Renault looked at the data and said no. Merc already know he's not the next big thing. The only question is, what do Merc want from their new driver? Someone who races Hamilton hard for the victories and can beat him but also is a safe enough hand to pick up the second places when they themselves get beat. Or someone who isn't going to challenge Lewis for the sake of team unity and an easy life.
One of those approaches can net you the WDC & the WCC, the other only the WDC. I don't think Merc are ready to give up on the WCC. I think it's get your wallet out time.
Danny, Fred, The finger. Maybe Sainz. That's the calibre they need and could maybe poach. (Danny by far the least likely) The child? Forget it.
Hulk, Pascal, Bottas. Not good enough when you have RB breathing down your neck with the distinct possibility of RB having as good or a better car as we move into an aero formula. Plus RB now have the strongest driver pairing in F1 by a country mile.
They need experience and speed. A proven talent that brings home the points. Who can you get, who is temptable. And which team would let a prized asset go for mega bucks. Which team could probably do with some extra cash, given their current constructors situation while they continue to lose their last few remaining sponsors?
Zak is new to Mclaren, He's pragmatic. He knows the project needs another five years to get them back to where they need to be, in the ring with a chance. He also knows Alonso won't be around by then to reap the rewards. Everyone knows that VD is their future, he is the man to win the McHonda championships. Let Alonso go have one last hurrah, use the extra cash from the deal to plug some holes till you can use that marketing genius to bring back the brands.
McLaren's place in the spotlight is coming but it's still a long way off. In the meantime to keep things ticking poach Perez back (lol) to be the experienced hand that drives the next few shitboxes. He's a different driver these days, more than enough of a safe pair of hands to bring in the points if not the prizes.
Zak, Toto, DO IT. Everyone wins.