Any way you slice it, McLaren made an offer, regardless of what that was, therefore it was Lewis's decision not to accept.
Unless McLaren made an offer that they knew Lewis wasn't going to take...
I have said this several times since Belgium: Lewis should consider himself lucky he was allowed to finish the season in McLaren, and was not put "on the street" effective immediately after what, no doubts, was a flagrant breach of contract, by twitting the team's telemetry after being beaten by Jenson in Belgium.
If anything, I would have been VERY disappointed that a big and glorious name as McLaren would have put their head down to the tantrums of one of their drivers.
Truth be told, Lewis is a terrific driver, but he is not a team player; and he is also not very effective in his conversion ratio. He should have won in 2007, 2008 and 2012. He only won one of these. And not thanks to his driving, but to the cheating that was taking place in Renault. Lewis can be very fast, and he can enjoy throwing hints at "I am like Senna" at every chance, but he is miles behind of being the great champion he promised during his rookie season.
And certainly, good luck at Mercedes! Brawn is not going to give him the nurturing and protective environment that Dennis provided. Good luck when twitting the telemetry after Rosberg qualifies better than him!