Its also on bbc...
http://www.bbc.com/sport/0/formula1/29638594
Imo he cannot risk to take a sabbatical, to return in 2016 hopping for a Mercedes seat, cause he might lose his form by then (as it also happened with other drivers), he is old enough to waste one year out, there is no guarantee that Mercedes will still be dominant by then and finally Mercedes will not let Lewis go and Rosberg has a contract until 2017.
Add to that, the fact McLaren haven't confirm their drivers yet, and Button seems frustrated in his last interviews, and Boullier says they could go for a big name or two for next year.
Since staying at Ferrari is out,
It's safe to say, that he's going to McLaren.