Money may have been a bit of a stumbling block in the negotiations though - due to having to pay for their Mercedes engines, they didn't have the budget to up or even equal his wages so he would have had to take a pay cut. Simple fact is that McLaren couldn't really afford him.
I reckon what's happened is (in very basic terms, without all the legal wrangles, endorsements etc) that Lewis said something along the lines of "Look guys, I've been to another team, they've offered me £x. If you can match it I'll stay". They couldn't and/or wouldn't so bye bye.
I have to say it's about time that a fresh face appeared in one of the top teams.
Wonder what price you would have got at the beginning of this season for Perez being at McLaren in 2013???