I think Alonso not only wants a 3rd championship, but wants it in a red car, so will stay for 2015, especially with the James Allison car potentially meaning Ferrari will be better next year - but then it's always next year with Ferrari
I'd say Button will drive McLaren or nothing - they could do much worse than to ditch him for Hulkenberg though. Button is a really nice guy whose character is likeable etc, but he simply doesn't have the pace.
Williams should do what they can to keep Bottas as he is showing very good skill, more so than Massa. I think Bottas > Massa > Button, so Williams signing the worst of the 3 drivers makes little sense to me. I can't see them having the funds for Massa and Button either if Bottas is tempted elsewhere, plus they'll want fresher blood.
If Mc-Honda do well in 2015, I can see Alonso moving there for 2016. This all depends on how much more he wants a Ferrari-championship than simply a 3rd championship in any car.
Then there is Vettel. He's been Red Bulls poster boy for a long time, but he's being shown up by the new kid on the block - is it enough to tempt him away, maybe moreso in 2016, especially with the last Newey car next year.
Similarly questions around Hamilton moving, but he'd be mad when he's in the best team this year who are looking very unlikely to be uncompetitive next!