McLaren are contracted with Mercedes up until 2015 which will see them to a 20 year relationship with Mercedes supplying the team since 1995. However over the last few years the relationship between McLaren and Mercedes has become more protracted. The end of the 2009 was the ideal time for Mercedes to buy into their own F1 project with McLaren entering the road car industry again and putting the two brands at odds. Mercedes up until this point had a 40% stake in McLaren which has been bought back by the latter with Mercedes now only having an 11% interest in the squad.
2013 was supposed to be the first year McLaren would have to purchase outright their F1 engines as Mercedes focus their sponsorship/money on the works team. So could this be the catalyst for the Lewis rumours and be a ploy by McLaren to continue to get free engines from Mercedes as a swan song for the releasing him into their care? With the 2014 engines muted to be costing significantly more than the current V8's even a driver as talented as Lewis has a price on his head and could be part of a much more protracted deal than most envisage.
Schumacher may not hold the only cards in this game either and could still stay at Mercedes with Nico going the other way as part of the deal. Lest we not forget that Paul Di Resta is also part of the Mercedes stable and with his recent change in management could find a seat amongst the McLaren or Mercedes ranks too making the whole situation very interesting indeed.
F1 at the core is really a business and so McLaren may be leveraging Lewis for their own gains, only time will tell but if the Eddie Jordan rumours are to be believed then I think solely looking at a decision made by Lewis may be fool hardy with so many other variables in play.