I think McLaren/Honda is probably Alonso's best punt for victory if he can't get a Red Bull or Mercedes seat (and he probably can't). Ferrari aren't going to hot next season with no chance of a radical update and their continuing record of mediocrity. Williams might be in with a chance but it's unlikely they'll be able to beat the team that makes their engines.
Bizarre comment: why would you need Button to do development when you've got Alonso?
This is a valid point if it's a choice between Alonso and Button - both have experience setting the car up so to replace one for the other isn't a problem.
Where I would be baffled, and I know I'm biased so bear with, is if Mclaren go for Alonso and Mag...
Let's just take stock here, yes Button has been out qualified by K-Mag this year, by a rookie no less, which isn't anything for Button's side to shout about, but let's also take a look at the points table - if Button had finished the GP on Sunday he'd currently be beating his team mate by TWICE as many points, at 80 or so points to 39. Kevin wouldn't have scored his one point if Jenson's car hadn't broke.
Beating his team mate by so many points, just like Jenson did to Perez, just shows that imo Mclaren would be mad to
not go for an (as stated above) POTENT driver pairing of Button and Alonso. Both are fast, both have exceptional race craft, whilst neither are amazing at single lap runs both know how to get the flag quickest given a decent car. Both are world champions so understand how to deal psychologically under pressure too.
Mclaren would have a MUCH better chance of winning the Constructor's Championship with But and Alo rather than Alo Mag, which is all they should be focused on. The engineering team needs to improve to make a better car so if I was Ron I'd be thinking about how to get as many points as possible rather than thinking about 3-5 year contract drivers with age on their side.