I don't buy the theory that Alonso could (or would even try to) stop Ferrari signing a top team mate. I think Alonso is a competitor and he must surely feel that his legacy has been tarnished by what happened against Lewis at McLaren. Santander loved having the pair together (a Spanish bank trying to be big in the UK) and it would save them a lot of money to have them both on one team as they could drop McLaren.
It might even be Lewis who has more to lose by going up against Fernando again. As it stands, he could argue he beat him ('cos he was a rookie). Yes, he could beat him again but does that prove anything? Maybe not, and the risk of losing to Fernando, especially after the struggles with Button last year must weigh heavily on Lewis.
Anyway, Andrew Benson's article on Lewis is very interesting
http://www.bbc.co.uk/blogs/andrewbenson/2012/05/will_hamilton_stay_at_mclaren.html. He is suggesting that Vettel may be bound for Ferrari as soon as 2014 which might mean Red Bull have to try and fill that vacancy, perhaps a year early by grabbing Lewis now for 2013 but that could be really complicated (much more I think than with Alonso).
I don't think he will drop to Lotus.
I don't think he will stay at McLaren - I think there is too much water under the bridge.
I guess it is possible that he could take a year out, spend some time in Monaco with Nicole enjoying his money? I can think of worse ways to spend a year
although I think she might want to get married
Otherwise, Mercedes? Maybe that depends on Schumacher and whether Brawn is ruthless enough and whether the Mercedes Benz board is committed enough to the sport. Assuming they are, this is what my cloudy crystal ball predicts.
Red Bull: Vettel,
Ferrari: Alonso, Webber
McLaren: Button, di Resta
Mercedes: Rosberg, Hamilton
Lotus: Raikkonen, Grosjean
Sauber: Perez, Kobayashi
Toro Rosso: Vergne, Ricciardo
Force India: Hulkenburg, Kartikeyan (if they are still in business)
Williams: Maldonado, Bottas
Caterham: Petrov, Razia
On the sidelines: Massa, Buemi, Alguersuari, Sutil, Kovaleinen & Schumacher
Hamilton is of course pivotal, but I think so too is Webber. If Ferrari do have their sights set on Alonso & Vettel for 2014/15 they might try and bring Perez in the mean time but he might not be in the right phase of his career to go up against Alonso. From what I can tell, he is quite wary of the prospect and if it looks like an interim drive, I can't see why he would. Webber looks to be the best bet for both parties for 1 or 2 years. Which would leave Red Bull really quite exposed as their young drivers are not really an improvement on the last batch... Maybe Perez?
I hope it shakes up anyway. We are into the third year with this combo in the top 8 cars aren't we?