I think personally, this decision has been made by Nico before.
Interstingly, it would explain what we saw this year happening; Mercedes simply helped Nico get that WDC.
There is a reasonable chance that Nico was concidering going to Ferrari to try getting the WDC there if he wouldn't get it @ Mercedes,
which would explain the talks there. So Mercedes took the offer and took a plan and it worked.
Lewis needs to correct his book now, lol.
I can respect his descision, but i'm really bummed out as I wanted to see what happens next year.
Also, someone has to say it: biggest chicken move in history? Grab the WDC and avoid any criticism next year if he wouldn't deliver?
So the Wehrlein non-contracting to me now makes a whole lot of sense @ Force India. 90% Certain he'll be the 2nd Merc driver now.
However, there are some possibilities though:
IF the Mclaren is not guaranteed winning car by now - and Alonso SHOULD have a decent view on the matter with development, testing, simulator work - I can see Alonso moving
mountains to go to Mercedes. With the changing conditions at Mclaren after the Ron Dennis departure, I can actually see more reason for that to happen. It would not do too much
good for his profile though, least he win and become WDC in 2017 with Mercedes - a big risk.
Vettel is another interesting theory. He is clearly not comfortable at Ferrari, and Mercedes would surely prefer Vettel over Wehrlein. Vettel is more experienced AND a 4 x WDC,
and next year aero plays a stronger role, which fits his style more. From anybody to choose from, Vettel would be the safest bet.
Vettel leaving Ferrari would free up a seat at Ferrari - interestingly. THE chance for Perez to say 'YOLO' or THE moment for Lewis to ditch Mercedes in favour of the Reds?
Risky move for Lewis. And secondly, risky for Mercedes too losing Hamilton - which they would create themselves by 'stealing' Vettel from Ferrari.
Then there's Perez. Perez would grab the opportunity. There is data available, they can know a lot through Force India. He's a probable safer bet than Wehrlein, BUT still a non-gp winner,
AND the question rises whether he fits the brand, and whether Mercedes would 'need' him - they dont need his sponsors that's for sure. It would however be interesting. Perez winning in Mercedes would completely sell out any LatinAmerican venue, would explode F1 into Mexico multiplied exponentially.
Finally, there's Ricciardo. Max is not going to Mercedes. surely not. [well i can be surprised at any point now]. Ricciardo PROBABLY wouldn't , because he doesn't want to play second fiddle to Lewis me thinks. But IF Ricky would go there. IF - then there again opens up the spot at RedBull. So WHO would go there?
I know most would scream blood and murder to put Sainz there, but there's the lingering problem of Sainz and Verstappen being a impossible combination.
So that would 'favour' Kvyat put back at RedBull - who got robbed of his seat anyway, so if we were to concider 'fairness' then Kvyat would be the fairest one to get that seat.
Which in itself would create a gigantic discussion either way - or 'worse' : Alonso @ Redbull alongside Max. imagine that.
i never thought Silly Season to come back with such a vengeance.
let's hope something shocking happens, and we don't get a 'meh' solution in the form of Werhlein.
I WANT BLOOD!!!
And Pascal was almost unsure of a drive next year with all the money staff that's going on at Manor!! Lucky boy 
Wow...what else 2016??
