Alonso will stay at Ferrari in my view. It's too risky to go to McLaren. The Honda engine could be a disaster, or it could be okay. I don't see it being a front running engine straight out of the blocks. The relationship with Ron Dennis would also be difficult.
I don't see how staying at Ferrari is any less risky than driving a McLaren-Honda would be in 2015. (In terms of winning F1 races)
The big question is what does Alonso want... does he want another championship? Does he want a Ferrari championship? Does he want to stick with something familiar, or does he need a change of scenery?